# Dakhlan’s Weblog

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## Sistem Koloid (2)

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Pengolahan Air Bersih

Pengolahan air bersih didasarkan pada sifat-sifat koloid, yaitu koagulasi dan adsorpsi. Air sungai atau air sumur yang keruh mengandung lumpur koloidal dan barangkali juga zat-zat warna, zat pencemar seperti limbah detergen dan pestisida. Bahan-bahan yang diperlukan untuk pengolahan air adalah tawas (alumunium sulfat), pasir, klorin atau kaporit, kapur tohor, dan karbon aktif. Tawas berguna untuk menggumpalkan lumpur koloidal sehingga mudah disaring. Tawas juga membentuk koloidal AL(OH)3 yang dapat mengadsorpsi zat-zat warna atau zat-zat pencemar seperti detergen dan pestisida. Apabila tingkat kekeruhan air yang diolah terlalu tinggi maka digunakan karbon aktif di samping tawas. Pasir berfungsi sebagai penyaring. Klorin atau kaporit berfungsi sebagai pembasmi hama (desinfektan), sedangkan kapur tohor berguna untuk menaikkan pH, yaitu untuk menetralkan keasaman ynang terjadi karena penggunaan trawas.

Industri Pengolahan Air Bersih (Perusahaan Air Minum)

Pengolahan air bersih di kota-kota besar pada prinsipnya sama dengan pengolahan air sederhana. Mula-mula air sungai dipompakan ke dalam bak prasedimentasi. Di sini lumpur dibiarkan mengendap karena pengaruh gravitasi. Lumpur dibuang dengan pompa, sedangkan air selanjutnya dialirkan ke dalam bak ventury. Pada tahap ini dicampurkan tawas dan gas klorin (preklorinasi). Poada air baku yang kekeruhan dan pencemarannya tinggi, perlu dibubuhkan karbon aktif yang berguna untuk menghilangkan bau, warna, rasa, dan zat organik yang terkandung dalam air baku. Dari bak ventury, air baku yang telah dicampur dengan bahan-bahan kimia dialirkan ke dalam accelator. Di dalam bak accelator ini terjadi proses koagulasi, lumpur dan kotoran lain menggumpal membentuk flok-flok yang akan mengalami sedimentasi secara gravitasi. Selanjutnya, air sudah setengah bersih dialirkan ke dalam bak saringan pasir. Pada saringan ini, sisa-sisa flok akan tertahan. Dari bak pasir diperoleh air yang sudah hampir bersih. Air yang sudah cukup bersih ini ditampung dalam bak lain yang disebut siphon, dimana ditambahkan kapur untuk menaikkan pH dan gas klorin (post klorinasi) untuk mematikan hama. Dari bak siphon, air yang sudah memenuhi standar air bersih selanjutnya dialirkan ke dalam reservoar, kemudian ke konsumen.

Pembuatan Sistem Koloid

Ukuran partikel-partikel koloid terletak antara partikel larutan sejati dan partikel suspensi. Oleh karena itu, sistem koloid dapat dibuat dengan pengelompokan (agregasi) partikel larutan sejati atau menghaluskan bahan dalam bentuk kasar kemudian didipersikan ke dalam medium pendispersi. Cara yang pertama disebut cara kondensasi, sedangkan yang kedua disebut cara dispersi.

Cara Kondensasi

Dengan cara kondensasi partikel larutan sejati (molekul atau ion) bergabung menjadi partikel koloid. Cara ini dapat dilakukan melalui reaksi-reaksi kimia, seperti reaksi redoks, hidrolisis, dan dekomposisi rangkap, atau dengan pergantian pelarut.

Reaksi Redoks

Reaksi redoks adalah reaksi yang disertai perubahan bilanga oksidasi.

Contoh 1:

Pembuatan sol belerang dari reaksi antara hidrogen sulfida (H2S) dengan belerang dioksida (SO2), yaitu dengan mengalirkan gas H2S ke dalam SO2.

2H2S(g) + SO2(aq) –> 2H2O(l) + 3 S(koloidal)

Contoh 2:

Pembuatan sol emas dari reaksi antara larutan HAuCl4 dengan larutan K2CO3 dan HCHO (formaldehida).

2HAuCl4(aq) + 6K2CO3(aq) + 3HCHO(aq) –> 2Au(koloidal) + 5CO2(g) + 8KCl(aq) + 3HCOOK(aq) + KHCO3(aq) + 2H2O (l)

Hidrolisis

Hidrolisis adalah reaksi suatu zat dengan air.

Contoh:

Pembuatan sol Fe(OH)3 dari hidrolisis FeCl3. Apabila ke dalam air mendidih ditambahkan larutan FeCl3 akan terbentuk sol Fe(OH)3.

FeCl3(aq) + 3H2O(l) –>Fe(OH)3(koloid) + 3 HCl(aq)

Dekomposisi Rangkap

Contoh 1:

Sol As2S3 dapat dibuat dari reaksi antara larutan H3AsO3 dengan larutan H2S.

2H3AsO3(aq) + 3H2S(aq) –> As2S3(koloid) + 6 H2O(l)

Contoh 2:

Sol AgCl dapat dibuat dengan mencampurkan larutan perak nitrat encer dengan larutan HCl encer.

AgNO3(aq) + HCl(aq) –> AgCl(koloid) + HNO3(aq)

Penggantian Pelarut

Selain dengan cara-cara kimia seperti di atas, koloid juga dapat terjadi dengan penggantian pelarut.

Contoh:

Apabila larutan jenuh kalsium asetat dicampur dengan alkohol akan terbentuk suatu koloid berupa gel.

Cara Dispersi

Dengan cara dispersi, partikel kasar dipecah menjadi partikel koloid. Cara dispersi dapat dilakukan secara mekanik, peptisasi atau dengan loncatan bunga listrik (cara busur Bredig).

Cara Mekanik

Menurut cara ini butir-butir kasar digerus dengan lumpang atau penggiling koloid sampai diperoleh tingkat kehalusan tertentu, kemudian diaduk dengan medium dispersi.

Contoh:

Sol belerang dapat dibuat dengan menggerus serbuk belerang bersama-sama dengan suatu zat inert (seperti gula pasir), kemudian mencampur serbuk halus itu dengan air.

Cara Peptisasi

Cara peptisasi adalah pembuatan koloid dari butir-butir kasar atau dari suatu endapan dengan bantuan suatu zat pemeptisasi (pemecah). Zat pemeptisasi memecahkan butir-butir kasar menjadi butir-butir koloid. Istilah peptisasi dikaitkan dengan peptonisasi, yaitu proses pemecahan protein (polipeptida) yang dikatalisis oleh enzim pepsin.

Contoh:

Agar-agar dipeptisasi oleh air, nitroselulosa oleh aseton, karet oleh bensin, dan lain-lain. Endapan NiS dipeptisasi oleh H2S dan endapan Al(OH)3 oleh AlCl3.

Cara Busur Bredig

Cara busur Bredig digunakan untuk membuat sol-sol logam. Logam yang akan dijadikan koloid digunakan sebagai elektrode yang dicelupkan dalam medium dispersi, kemudian diberi loncatan listrik di antara kedua ujungnya. Mula-mula atom-atom logam akan terlempar ke dalam air, lalu atom-atom tersebut mengalami kondensasi sehingga membentuk partikel koloid. Jadi, cara busur ini merupakan gabungan cara dispersi dan cara kondensasi.

Koloid Asosiasi

Berbagai jenis zat, seperti sabun dan detergen, larut dalam air tetapi tidak membentuk larutan, melainkan koloid. Molekul sabun atau detergen terdiri atas bagian yang polar (disebut kepala) dan bagian yang nonpolar (disebut ekor).

CH3 –CH2 –CH2 –CH2 –CH2 –CH2 –CH2 –CH2 –CH2 –CH2 –CH2 –CH2 –CH2 –CH2

Ekor

O

ll

–CH2 – C -ONa+

Kepala

Kepala sabun adalah gugus yang hidrofil (tertarik ke air) sedangkan gugus hidrokarbon bersifat hidrpfob (takut air). Jika sabun dilarutkan dalam air, maka molekul-molekul sabun akan mengadakan asosiasi karena gugus nonpolarnya (ekor) saling tarik-menarik, sehingga terbentuk partikel koloid.

Daya pengemulsi dari sabun dan detergen juga disebabkan oleh aksi yang sama. Gugus nonpolar dari sabun akan menarik partikel kotoran (lemak) dari bahan cucian kemudian mendispersikannya ke dalam air.

Sebagai bahan pencuci, sabun dan detergen bukan saja berfungsi sebagai pengemulsi tetapi juga sebagai pembasah atau penurun tegangan permukaan. Air yang mengandung sabun atau detergen mempunyai tegangan permukaan yang lebih rendah sehingga lebih mudah meresap pada bahan cucian.

Koloid dan Polusi

Berbagai masalah lingkungan terkait dengan koloid, di antaranya adalah asbut. Sebanyak 4000 orang meninggal dalam kasus asbut di London pada tahun 1952. Asbut adalah campuran yang rumit yang terdiri atas berbagai gas dan partikel-partikel zat cair dan zat padat. Asbut (smog) merupakan kombinasi dari asap (smoke) dan kabut (fog).

Kabut sendiri merupakan dispersi partikel air dalam udara. Kabut terjadi jika udara panas yang mengandung uap air tiba-tiba mengalami pendinginan, sehingga sebagian uap air mengalami kondensasi. Jika asap bergabung dengan kabut, maka kabut menghalangi asap naik. Akibatnya, asap tetap berada di sekitar kita dan kita menghirupnya.

Asap mengandung partikel yang dapat mengiritasi paru-paru dan membuat kita batuk. Asap juga mengandung belerang dioksida (SO2). Gas ini dapat bereaksi dengan oksigen dan uap air membentuk asam sulfat. Asam sulfat akan mengiritasi paru-paru sehingga menghasilkan banyak lendir.

Selain itu, asbut mengandung berbagai jenis gas yang terbentuk dari serentetan reaksi fotokimia (yaitu reaksi kimia yang berlangsung di bawah pengaruh sinar matahari). Di antaranya, yaitu ozon, aldehida, dan peroksiasetil nitrat (PAN = CH3 –COOONO2).

Sumber: Buku Paket Kimia Erlangga SMA Kelas XI

Mei 2, 2009 Posted by | Uncategorized | Tinggalkan komentar

## Joke

Internet magic

Two teenagers decided to introduce their elderly mother to the magic of the internet. The first move was to access the popular Ask Jeeves website. They told her it could answer any question she had.

The mother was very skeptical until one of the teens said, “It,s true, Mom. Think of something to ask.” After about a minute thought, the mother then responded, “How is Aunt Helen feeling?”

Car Privileges

The mother and father had just given their teenage daughter family-car privileges. On Saturday night she returned home very late from a party.

The next morning her father went out to the driveway to get the newspaper and came back into the house frowning. At 11:30 AM the girl sleepily walked into the kitchen, and her father asked her, “Sweetheart, what time did you get in last night?”

“Not too late, Dad,” she replied nervously.

Calmly, her father said, “Then, honey, I’ll have to talk with the paperboy about putting my paper under the front tire of the car.”

— All men are idiots, and I married their king.
— Your kid may be an honors student, but you’re still an idiot.
— I brake for no apparent reason.
— Time is what keeps everything from happening all at once.
— Out of my mind. Back in five minutes.
— I didn’t fight my way to the top of the food chain to be a vegetarian.
— Women who seek to be equal to men lack ambition.
— Reality is a crutch for people who can’t handle drugs.
— I don’t suffer from insanity, I enjoy every minute of it.
— Hard work pays off in the future. Laziness pays off NOW.
— Give me ambiguity or give me something else.
— Always remember you’re unique, just like everyone else.
— Puritanism: the haunting fear that someone somewhere may be happy.
— Consciousness cuts into my napping.
— Beauty is in the eye of the beer holder.
— There are 3 kinds of people: those who can count and those who can’t.

I’m getting a new car. You know what kind of car I’m getting? I’m getting a Honda Civic because those are very safe cars. And I know ’cause I saw a guy total one the other day when I ran him off the road.

Harry and Martha drank their coffee as they listened to the morning weather report.

“There will be three to five inches of snow today. You must park your cars on the odd-numbered side of the street.”

Harry got up from his coffee to move the car.

Two days later, they sat down with their cup of coffee and listened the weather forecast.

“There will be two to four inches of snow today. You must park your cars on the even-numbered side of the street.”

Harry got up from his coffee to move the car.

Three days later, they tuned in to the weather report.

“There will be six to eight inches of snow today. You must park your cars on the….” The power went off.

He said to Martha, “What am I going to do now?”

Martha said, “Just leave the car in the garage.”

source: http://www.jokes.com

April 28, 2009 Posted by | Uncategorized | Tinggalkan komentar

## Plato’s account

Plato’s dialogues Timaeus and Critias, written in 360 BC, contain the earliest references to Atlantis. For unknown reasons, Plato never completed Critias; however, the scholar Benjamin Jowett, among others, argues that Plato originally planned a third dialogue titled Hermocrates. John V. Luce assumes that Plato, after describing the origin of the world and mankind in Timaeus and the allegorical perfect society of ancient Athens and its successful defense against an antagonistic Atlantis in Critias, would have made the strategy of the Greek civilization during their conflict with the Persians a subject of discussion in the Hermocrates. Plato introduced Atlantis in Timaeus:

For it is related in our records how once upon a time your State stayed the course of a mighty host, which, starting from a distant point in the Atlantic ocean, was insolently advancing to attack the whole of Europe, and Asia to boot. For the ocean there was at that time navigable; for in front of the mouth which you Greeks call, as you say, ‘the pillars of Heracles,’ there lay an island which was larger than Libya and Asia together; and it was possible for the travelers of that time to cross from it to the other islands, and from the islands to the whole of the continent over against them which encompasses that veritable ocean. For all that we have here, lying within the mouth of which we speak, is evidently a haven having a narrow entrance; but that yonder is a real ocean, and the land surrounding it may most rightly be called, in the fullest and truest sense, a continent. Now in this island of Atlantis there existed a confederation of kings, of great and marvelous power, which held sway over all the island, and over many other islands also and parts of the continent.

The four persons appearing in those two dialogues are the politicians Critias and Hermocrates as well as the philosophers Socrates and Timaeus of Locri, although only Critias speaks of Atlantis. While most likely all of these people actually lived, these dialogues, written as if recorded, may have been the invention of Plato. In his works Plato makes extensive use of the Socratic dialogues in order to discuss contrary positions within the context of a supposition.

The Timaeus begins with an introduction, followed by an account of the creations and structure of the universe and ancient civilizations. In the introduction, Socrates muses about the perfect society, described in Plato’s Republic (ca. 380 BC), and wonders if he and his guests might recollect a story which exemplifies such a society. Critias mentions an allegedly historical tale that would make the perfect example, and follows by describing Atlantis as is recorded in the Critias. In his account, ancient Athens seems to represent the “perfect society” and Atlantis its opponent, representing the very antithesis of the “perfect” traits described in the Republic. Critias claims that his accounts of ancient Athens and Atlantis stem from a visit to Egypt by the legendary Athenian lawgiver Solon in the 6th century BC. In Egypt, Solon met a priest of Sais, who translated the history of ancient Athens and Atlantis, recorded on papyri in Egyptian hieroglyphs, into Greek. According to Plutarch, Solon met with “Psenophis of Heliopolis, and Sonchis the Saite, the most learned of all the priests”;[5] Plutarch refers here to events that would have happened five centuries before he wrote of them.

According to Critias, the Hellenic gods of old divided the land so that each god might own a lot; Poseidon was appropriately, and to his liking, bequeathed the island of Atlantis. The island was larger than Ancient Libya and Asia Minor combined, but it afterwards was sunk by an earthquake and became an impassable mud shoal, inhibiting travel to any part of the ocean. The Egyptians, Plato asserted, described Atlantis as an island comprising mostly mountains in the northern portions and along the shore, and encompassing a great plain of an oblong shape in the south “extending in one direction three thousand stadia [about 555 km; 345 mi], but across the center inland it was two thousand stadia [about 370 km; 230 mi].” Fifty stadia [9 km; 6 mi] from the coast was a mountain that was low on all sides…broke it off all round about … the central island itself was five stades in diameter [about 0.92 km; 0.57 mi].

In Plato’s myth, Poseidon fell in love with Cleito, the daughter of Evenor and Leucippe, who bore him five pairs of male twins. The eldest of these, Atlas, was made rightful king of the entire island and the ocean (called the Atlantic Ocean in his honor), and was given the mountain of his birth and the surrounding area as his fiefdom. Atlas’s twin Gadeirus, or Eumelus in Greek, was given the extremity of the island towards the Pillars of Heracles. The other four pairs of twins — Ampheres and Evaemon, Mneseus and Autochthon, Elasippus and Mestor, and Azaes and Diaprepes — were also given “rule over many men, and a large territory.”

Poseidon carved the mountain where his love dwelt into a palace and enclosed it with three circular moats of increasing width, varying from one to three stadia and separated by rings of land proportional in size. The Atlanteans then built bridges northward from the mountain, making a route to the rest of the island. They dug a great canal to the sea, and alongside the bridges carved tunnels into the rings of rock so that ships could pass into the city around the mountain; they carved docks from the rock walls of the moats. Every passage to the city was guarded by gates and towers, and a wall surrounded each of the city’s rings. The walls were constructed of red, white and black rock quarried from the moats, and were covered with brass, tin and the precious metal orichalcum, respectively.

According to Critias, 9,000 years before his lifetime a war took place between those outside the Pillars of Hercules at the Strait of Gibraltar and those who dwelt within them. The Atlanteans had conquered the parts of Libya within the Pillars of Heracles as far as Egypt and the European continent as far as Tyrrhenia, and subjected its people to slavery. The Athenians led an alliance of resistors against the Atlantean empire, and as the alliance disintegrated, prevailed alone against the empire, liberating the occupied lands.

But at a later time there occurred portentous earthquakes and floods, and one grievous day and night befell them, when the whole body of your warriors was swallowed up by the earth, and the island of Atlantis in like manner was swallowed up by the sea and vanished; wherefore also the ocean at that spot has now become impassable and unsearchable, being blocked up by the shoal mud which the island created as it settled down.

Source: wikipedia

April 28, 2009 Posted by | Uncategorized | Tinggalkan komentar

## Elementary properties of superconductors

Most of the physical properties of superconductors vary from material to material, such as the heat capacity and the critical temperature, critical field, and critical current density at which superconductivity is destroyed.

On the other hand, there is a class of properties that are independent of the underlying material. For instance, all superconductors have exactly zero resistivity to low applied currents when there is no magnetic field present. The existence of these “universal” properties implies that superconductivity is a thermodynamic phase, and thus possess certain distinguishing properties which are largely independent of microscopic details.

### Zero electrical “dc” resistance

Electric cables for accelerators at CERN: top, regular cables for LEP; bottom, superconducting cables for the LHC.

The simplest method to measure the electrical resistance of a sample of some material is to place it in an electrical circuit in series with a current source I and measure the resulting voltage V across the sample. The resistance of the sample is given by Ohm’s law as $R = \frac{V}{I}$. . If the voltage is zero, this means that the resistance is zero and that the sample is in the superconducting state.

Superconductors are also able to maintain a current with no applied voltage whatsoever, a property exploited in superconducting electromagnets such as those found in MRI machines. Experiments have demonstrated that currents in superconducting coils can persist for years without any measurable degradation. Experimental evidence points to a current lifetime of at least 100,000 years. Theoretical estimates for the lifetime of a persistent current can exceed the estimated lifetime of the universe, depending on the wire geometry and the temperature. Thus, a superconductor does not have exactly zero resistance, however, the resistance is negligibly small.

In a normal conductor, an electrical current may be visualized as a fluid of electrons moving across a heavy ionic lattice. The electrons are constantly colliding with the ions in the lattice, and during each collision some of the energy carried by the current is absorbed by the lattice and converted into heat, which is essentially the vibrational kinetic energy of the lattice ions. As a result, the energy carried by the current is constantly being dissipated. This is the phenomenon of electrical resistance.

The situation is different in a superconductor. In a conventional superconductor, the electronic fluid cannot be resolved into individual electrons. Instead, it consists of bound pairs of electrons known as Cooper pairs. This pairing is caused by an attractive force between electrons from the exchange of phonons. Due to quantum mechanics, the energy spectrum of this Cooper pair fluid possesses an energy gap, meaning there is a minimum amount of energy ΔE that must be supplied in order to excite the fluid. Therefore, if ΔE is larger than the thermal energy of the lattice, given by kT, where k is Boltzmann’s constant and T is the temperature, the fluid will not be scattered by the lattice. The Cooper pair fluid is thus a superfluid, meaning it can flow without energy dissipation.

In a class of superconductors known as Type II superconductors, including all known high-temperature superconductors, an extremely small amount of resistivity appears at temperatures not too far below the nominal superconducting transition when an electrical current is applied in conjunction with a strong magnetic field, which may be caused by the electrical current. This is due to the motion of vortices in the electronic superfluid, which dissipates some of the energy carried by the current. If the current is sufficiently small, the vortices are stationary, and the resistivity vanishes. The resistance due to this effect is tiny compared with that of non-superconducting materials, but must be taken into account in sensitive experiments. However, as the temperature decreases far enough below the nominal superconducting transition, these vortices can become frozen into a disordered but stationary phase known as a “vortex glass”. Below this vortex glass transition temperature, the resistance of the material becomes truly zero.

### Superconducting phase transition

In superconducting materials, the characteristics of superconductivity appear when the temperature T is lowered below a critical temperature Tc. The value of this critical temperature varies from material to material. Conventional superconductors usually have critical temperatures ranging from around 20 K (kelvins) to less than 1 K. Solid mercury, for example, has a critical temperature of 4.2 K. As of 2001, the highest critical temperature found for a conventional superconductor is 39 K for magnesium diboride (MgB2)[2], although this material displays enough exotic properties that there is doubt about classifying it as a “conventional” superconductor. Cuprate superconductors can have much higher critical temperatures: YBa2Cu3O7, one of the first cuprate superconductors to be discovered, has a critical temperature of 92 K, and mercury-based cuprates have been found with critical temperatures in excess of 130 K. The explanation for these high critical temperatures remains unknown. Electron pairing due to phonon exchanges explains superconductivity in conventional superconductors, but it does not explain superconductivity in the newer superconductors that have a very high critical temperature.

Similarly, at a fixed temperature below the critical temperature, superconducting materials cease to superconduct when an external magnetic field is applied which is greater than the critical magnetic field. This is because the Gibbs free energy of the superconducting phase increases quadratically with the magnetic field while the free energy of the normal phase is roughly independent of the magnetic field. If the material superconducts in the absence of a field, then the superconducting phase free energy is lower than that of the normal phase and so for some finite value of the magnetic field (proportional to the square root of the difference of the free energies at zero magnetic field) the two free energies will be equal and a phase transition to the normal phase will occur. More generally, a higher temperature and a stronger magnetic field lead to a smaller fraction of the electrons in the superconducting band and consequently a longer London penetration depth of external magnetic fields and currents. The penetration depth becomes infinite at the phase transition.

The onset of superconductivity is accompanied by abrupt changes in various physical properties, which is the hallmark of a phase transition. For example, the electronic heat capacity is proportional to the temperature in the normal (non-superconducting) regime. At the superconducting transition, it suffers a discontinuous jump and thereafter ceases to be linear. At low temperatures, it varies instead as e−α /T for some constant α. This exponential behavior is one of the pieces of evidence for the existence of the energy gap.

The order of the superconducting phase transition was long a matter of debate. Experiments indicate that the transition is second-order, meaning there is no latent heat. However in the presence of an external magnetic field there is latent heat, as a result of the fact that the superconducting phase has a lower entropy below the critical temperature than the normal phase. It has experimentally demonstrated  that, as a consequence, when the magnetic field is increased beyond the critical field, the resulting phase transition leads to a decrease in the temperature of the superconducting material.

Calculations in the 1970s suggested that it may actually be weakly first-order due to the effect of long-range fluctuations in the electromagnetic field. In the 1980s it was shown theoretically with the help of a disorder field theory, in which the vortex lines of the superconductor play a major role, that the transition is of second order within the type II regime and of first order (i.e., latent heat) within the type I regime, and that the two regions are separated by a tricritical point The results were confirmed by Monte Carlo computer simulations in Ref.

Source: wikipedia

April 28, 2009 Posted by | Uncategorized | Tinggalkan komentar

## Albert Einstein

Albert Einstein (German: ; English: /ˈælbərt ˈaɪnstaɪn/; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist. He is best known for his theory of relativity and specifically mass–energy equivalence, expressed by the equation Emc2. Einstein received the 1921 Nobel Prize in Physics “for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect.”

Einstein’s many contributions to physics include:

Einstein published more than 300 scientific works and more than 150 non-scientific works. In 1999 Time magazine named him the “Person of the Century“, and in the words of Einstein biographer Don Howard, “to the scientifically literate and the public at large, Einstein is synonymous with genius.”

## Patent office

The ‘Einsteinhaus’ on the Kramgasse in Berne where Einstein lived with Mileva on the first floor during his Annus Mirabilis

Following graduation, Einstein could not find a teaching post. After almost two years of searching, a former classmate’s father helped him get a job in Berne, at the Federal Office for Intellectual Property,[14] the patent office, as an assistant examiner. His responsibility was evaluating patent applications for electromagnetic devices. In 1903, Einstein’s position at the Swiss Patent Office was made permanent, although he was passed over for promotion until he “fully mastered machine technology”.

With friends he met in Berne, Einstein formed a weekly discussion club on science and philosophy, jokingly named “The Olympia Academy“. Their readings included Poincaré, Mach, and Hume, who influenced Einstein’s scientific and philosophical outlook.

During this period Einstein had almost no personal contact with the physics community. Much of his work at the patent office related to questions about transmission of electric signals and electrical-mechanical synchronization of time: two technical problems that show up conspicuously in the thought experiments that eventually led Einstein to his radical conclusions about the nature of light and the fundamental connection between space and time.

## Marriage and family life

Einstein and Mileva Marić had a daughter they called Lieserl, who was born in early 1902, probably in Novi Sad. Her fate is uncertain after 1903.

Einstein married Mileva on 6 January 1903, although his mother had objected to the match because she had a prejudice against Serbs and thought Marić “too old” and “physically defective.”[19] [20] Their relationship was for a time a personal and intellectual partnership. In a letter to her, Einstein called Marić “a creature who is my equal and who is as strong and independent as I am.” There has been occasional debate about whether Marić influenced Einstein’s work, however, the overwhelming consensus amongst academic historians of science is that she did not. On 14 May 1904, Albert and Mileva’s first son, Hans Albert Einstein, was born in Berne, Switzerland. Their second son, Eduard, was born in Zurich on 28 July 1910.

Albert and Marić divorced on 14 February 1919, having lived apart for five years. On 2 June of that year, Einstein married Elsa Löwenthal (née Einstein), who had nursed him through an illness. Elsa was Albert’s first cousin maternally and his second cousin paternally. Together the Einsteins raised Margot and Ilse, Elsa’s daughters from her first marriage. Their union produced no children.

## Annus Mirabilis and special relativity

Albert Einstein, 1905

In 1905, while he was working in the patent office, Einstein had four papers published in the Annalen der Physik, the leading German physics journal. These are the papers that history has come to call the Annus Mirabilis Papers:

• His paper on the particulate nature of light put forward the idea that certain experimental results, notably the photoelectric effect, could be simply understood from the postulate that light interacts with matter as discrete “packets” (quanta) of energy, an idea that had been introduced by Max Planck in 1900 as a purely mathematical manipulation, and which seemed to contradict contemporary wave theories of light .
• His paper on Brownian motion explained the random movement of very small objects as direct evidence of molecular action, thus supporting the atomic theory.
• His paper on the electrodynamics of moving bodies introduced the radical theory of special relativity, which showed that the observed independence of the speed of light on the observer’s state of motion required fundamental changes to the notion of simultaneity. Consequences of this include the time-space frame of a moving body slowing down and contracting (in the direction of motion) relative to the frame of the observer. This paper also argued that the idea of a luminiferous aether—one of the leading theoretical entities in physics at the time—was superfluous.
• In his paper on mass–energy equivalence (previously considered to be distinct concepts), Einstein deduced from his equations of special relativity what has been called the twentieth century’s most well known equation: Emc2. This suggests that tiny amounts of mass could be converted into huge amounts of energy and presaged the development of nuclear power.

All four papers are today recognized as tremendous achievements—and hence 1905 is known as Einstein’s “Wonderful Year“. At the time, however, they were not noticed by most physicists as being important, and many of those who did notice them rejected them outright. Some of this work—such as the theory of light quanta—remained controversial for years.

At the age of 26, having studied under Alfred Kleiner, Professor of Experimental Physics, Einstein was awarded a PhD by the University of Zurich. His dissertation was entitled A New Determination of Molecular Dimensions.

source: wikipedia

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## Biotechnology

Insulin crystals.

Biotechnology is technology based on biology, especially when used in agriculture, food science, and medicine. United Nations Convention on Biological Diversity defines biotechnology as:

Any technological application that uses biological systems, living organisms, or derivatives thereof, to make or modify products or processes for specific use.

Biotechnology is often used to refer to genetic engineering technology of the 21st century, however the term encompasses a wider range and history of procedures for modifying biological organisms according to the needs of humanity, going back to the initial modifications of native plants into improved food crops through artificial selection and hybridization. Bioengineering is the science upon which all biotechnological applications are based. With the development of new approaches and modern techniques, traditional biotechnology industries are also acquiring new horizons enabling them to improve the quality of their products and increase the productivity of their systems.

Before 1971, the term, biotechnology, was primarily used in the food processing and agriculture industries. Since the 1970s, it began to be used by the Western scientific establishment to refer to laboratory-based techniques being developed in biological research, such as recombinant DNA or tissue culture-based processes, or horizontal gene transfer in living plants, using vectors such as the Agrobacterium bacteria to transfer DNA into a host organism. In fact, the term should be used in a much broader sense to describe the whole range of methods, both ancient and modern, used to manipulate organic materials to reach the demands of food production. So the term could be defined as, “The application of indigenous and/or scientific knowledge to the management of (parts of) microorganisms, or of cells and tissues of higher organisms, so that these supply goods and services of use to the food industry and its consumers.[2]

Biotechnology combines disciplines like genetics, molecular biology, biochemistry, embryology and cell biology, which are in turn linked to practical disciplines like chemical engineering, information technology, and biorobotics. Patho-biotechnology describes the exploitation of pathogens or pathogen derived compounds for beneficial effect.

Although not normally thought of as biotechnology, agriculture clearly fits the broad definition of “using a biological system to make products” such that the cultivation of plants may be viewed as the earliest biotechnological enterprise. Agriculture has been theorized to have become the dominant way of producing food since the Neolithic Revolution. The processes and methods of agriculture have been refined by other mechanical and biological sciences since its inception. Through early biotechnology, farmers were able to select the best suited and highest-yield crops to produce enough food to support a growing population. Other uses of biotechnology were required as crops and fields became increasingly large and difficult to maintain. Specific organisms and organism by-products were used to fertilize, restore nitrogen, and control pests. Throughout the use of agriculture, farmers have inadvertently altered the genetics of their crops through introducing them to new environments and breeding them with other plants–one of the first forms of biotechnology. Cultures such as those in Mesopotamia, Egypt, and India developed the process of brewing beer. It is still done by the same basic method of using malted grains (containing enzymes) to convert starch from grains into sugar and then adding specific yeasts to produce beer. In this process the carbohydrates in the grains were broken down into alcohols such as ethanol. Ancient Indians also used the juices of the plant Ephedra vulgaris and used to call it Soma. Later other cultures produced the process of Lactic acid fermentation which allowed the fermentation and preservation of other forms of food. Fermentation was also used in this time period to produce leavened bread. Although the process of fermentation was not fully understood until Louis Pasteur’s work in 1857, it is still the first use of biotechnology to convert a food source into another form.

Combinations of plants and other organisms were used as medications in many early civilizations. Since as early as 200 BC, people began to use disabled or minute amounts of infectious agents to immunize themselves against infections. These and similar processes have been refined in modern medicine and have led to many developments such as antibiotics, vaccines, and other methods of fighting sickness.

In the early twentieth century scientists gained a greater understanding of microbiology and explored ways of manufacturing specific products. In 1917, Chaim Weizmann first used a pure microbiological culture in an industrial process, that of manufacturing corn starch using Clostridium acetobutylicum, to produce acetone, which the United Kingdom desperately needed to manufacture explosives during World War I.

The field of modern biotechnology is thought to have largely begun on , when the United States Supreme Court ruled that a genetically-modified microorganism could be patented in the case of Diamond v. Chakrabarty. Indian-born Ananda Chakrabarty, working for General Electric, had developed a bacterium (derived from the Pseudomonas genus) capable of breaking down crude oil, which he proposed to use in treating oil spills.

Revenue in the industry is expected to grow by 12.9% in 2008. Another factor influencing the biotechnology sector’s success is improved intellectual property rights legislation — and enforcement — worldwide, as well as strengthened demand for medical and pharmaceutical products to cope with an ageing, and ailing, U.S. population.

Rising demand for biofuels is expected to be good news for the biotechnology sector, with the Department of Energy estimating ethanol usage could reduce U.S. petroleum-derived fuel consumption by up to 30% by 2030. The biotechnology sector has allowed the U.S. farming industry to rapidly increase its supply of corn and soybeans — the main inputs into biofuels — by developing genetically-modified seeds which are resistant to pests and drought. By boosting farm productivity, biotechnology plays a crucial role in ensuring that biofuel production targets are met.

Source: Wikipedia

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## Atom

Helium atom

The atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of Hydrogen-1, which is the only stable nuclide with no neutron). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it has a positive or negative charge and is an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determine the isotope of the element.

The name atom comes from the Greek τομος/átomos, α-τεμνω, which means uncuttable, something that cannot be divided further. The concept of an atom as an indivisible component of matter was first proposed by early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that certain substances could not be further broken down by chemical methods. During the late 19th and early 20th centuries, physicists discovered subatomic components and structure inside the atom, thereby demonstrating that the ‘atom’ was not indivisible. The principles of quantum mechanics were used to successfully model the atom.[1][2]

Relative to everyday experience, atoms are minuscule objects with proportionately tiny masses. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.9% of an atom’s mass is concentrated in the nucleus,[note 1] with protons and neutrons having roughly equal mass. Each element has at least one isotope with unstable nuclei that can undergo radioactive decay. This can result in a transmutation that changes the number of protons or neutrons in a nucleus.[3] Electrons that are bound to atoms possess a set of stable energy levels, or orbitals, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels. The electrons determine the chemical properties of an element, and strongly influence an atom’s magnetic properties.

### Subatomic particles

Though the word atom originally denoted a particle that cannot be cut into smaller particles, in modern scientific usage the atom is composed of various subatomic particles. The constituent particles of an atom are the electron, the proton and the neutron. However, the hydrogen-1 atom has no neutrons and a positive hydrogen ion has no electrons.

The electron is by far the least massive of these particles at 9.11 × 10−31 kg, with a negative electrical charge and a size that is too small to be measured using available techniques.[34] Protons have a positive charge and a mass 1,836 times that of the electron, at 1.6726 × 10−27 kg, although this can be reduced by changes to the energy binding the proton into an atom. Neutrons have no electrical charge and have a free mass of 1,839 times the mass of electrons, or 1.6929 × 10−27 kg. Neutrons and protons have comparable dimensions—on the order of 2.5 × 10−15 m—although the ‘surface’ of these particles is not sharply defined.

In the Standard Model of physics, both protons and neutrons are composed of elementary particles called quarks. The quark belongs to the fermion group of particles, and is one of the two basic constituents of matter—the other being the lepton, of which the electron is an example. There are six types of quarks, each having a fractional electric charge of either +2/3 or −1/3. Protons are composed of two up quarks and one down quark, while a neutron consists of one up quark and two down quarks. This distinction accounts for the difference in mass and charge between the two particles. The quarks are held together by the strong nuclear force, which is mediated by gluons. The gluon is a member of the family of gauge bosons, which are elementary particles that mediate physical forces.

### Nucleus

The binding energy needed for a nucleon to escape the nucleus, for various isotopes.

All the bound protons and neutrons in an atom make up a tiny atomic nucleus, and are collectively called nucleons. The radius of a nucleus is approximately equal to $\begin{smallmatrix}1.07 \sqrt[3]{A}\end{smallmatrix}$ fm, where A is the total number of nucleons.[39] This is much smaller than the radius of the atom, which is on the order of 105 fm. The nucleons are bound together by a short-ranged attractive potential called the residual strong force. At distances smaller than 2.5 fm this force is much more powerful than the electrostatic force that causes positively charged protons to repel each other.[40]

Atoms of the same element have the same number of protons, called the atomic number. Within a single element, the number of neutrons may vary, determining the isotope of that element. The total number of protons and neutrons determine the nuclide. The number of neutrons relative to the protons determines the stability of the nucleus, with certain isotopes undergoing radioactive decay.[41]

The neutron and the proton are different types of fermions. The Pauli exclusion principle is a quantum mechanical effect that prohibits identical fermions (such as multiple protons) from occupying the same quantum physical state at the same time. Thus every proton in the nucleus must occupy a different state, with its own energy level, and the same rule applies to all of the neutrons. (This prohibition does not apply to a proton and neutron occupying the same quantum state.)[42]

For atoms with low atomic numbers, a nucleus that has a different number of protons than neutrons can potentially drop to a lower energy state through a radioactive decay that causes the number of protons and neutrons to more closely match. As a result, atoms with roughly matching numbers of protons and neutrons are more stable against decay. However, with increasing atomic number, the mutual repulsion of the protons requires an increasing proportion of neutrons to maintain the stability of the nucleus, which modifies this trend. Thus, there are no stable nuclei with equal proton and neutron numbers above atomic number Z = 20 (calcium); and as Z increases toward the heaviest nuclei, the ratio of neutrons per proton required for stability increases to about 1.5.

Illustration of a nuclear fusion process that forms a deuterium nucleus, consisting of a proton and a neutron, from two protons. A positron (e+)—an antimatter electron—is emitted along with an electron neutrino.

The number of protons and neutrons in the atomic nucleus can be modified, although this can require very high energies because of the strong force. Nuclear fusion occurs when multiple atomic particles join to form a heavier nucleus, such as through the energetic collision of two nuclei. For example, at the core of the Sun protons require energies of 3–10 keV to overcome their mutual repulsion—the coulomb barrier—and fuse together into a single nucleus. Nuclear fission is the opposite process, causing a nucleus to split into two smaller nuclei—usually through radioactive decay. The nucleus can also be modified through bombardment by high energy subatomic particles or photons. If this modifies the number of protons in a nucleus, the atom changes to a different chemical element.

If the mass of the nucleus following a fusion reaction is less than the sum of the masses of the separate particles, then the difference between these two values is emitted as energy, as described by Albert Einstein‘s mass–energy equivalence formula, Emc2, where m is the mass loss and c is the speed of light. This deficit is the binding energy of the nucleus.

The fusion of two nuclei that have lower atomic numbers than iron and nickel is usually an exothermic process that releases more energy than is required to bring them together. It is this energy-releasing process that makes nuclear fusion in stars a self-sustaining reaction. For heavier nuclei, the total binding energy begins to decrease. That means fusion processes with nuclei that have higher atomic numbers is an endothermic process. These more massive nuclei can not undergo an energy-producing fusion reaction that can sustain the hydrostatic equilibrium of a star.

### Electron cloud

A potential well, showing the minimum energy V(x) needed to reach each position x. A particle with energy E is constrained to a range of positions between x1 and x2.

The electrons in an atom are attracted to the protons in the nucleus by the electromagnetic force. This force binds the electrons inside an electrostatic potential well surrounding the smaller nucleus, which means that an external source of energy is needed in order for the electron to escape. The closer an electron is to the nucleus, the greater the attractive force. Hence electrons bound near the center of the potential well require more energy to escape than those at greater separations.

Electrons, like other particles, have properties of both a particle and a wave. The electron cloud is a region inside the potential well where each electron forms a type of three-dimensional standing wave—a wave form that does not move relative to the nucleus. This behavior is defined by an atomic orbital, a mathematical function that characterises the probability that an electron will appear to be at a particular location when its position is measured. Only a discrete (or quantized) set of these orbitals exist around the nucleus, as other possible wave patterns will rapidly decay into a more stable form. Orbitals can have one or more ring or node structures, and they differ from each other in size, shape and orientation.

Wave functions of the first five atomic orbitals. The three 2p orbitals each display a single angular node that has an orientation and a minimum at the center.

Each atomic orbital corresponds to a particular energy level of the electron. The electron can change its state to a higher energy level by absorbing a photon with sufficient energy to boost it into the new quantum state. Likewise, through spontaneous emission, an electron in a higher energy state can drop to a lower energy state while radiating the excess energy as a photon. These characteristic energy values, defined by the differences in the energies of the quantum states, are responsible for atomic spectral lines.

The amount of energy needed to remove or add an electron (the electron binding energy) is far less than the binding energy of nucleons. For example, it requires only 13.6 eV to strip a ground-state electron from a hydrogen atom, compared to 2.23 Mev for splitting a deuterium nucleus. Atoms are electrically neutral if they have an equal number of protons and electrons. Atoms that have either a deficit or a surplus of electrons are called ions. Electrons that are farthest from the nucleus may be transferred to other nearby atoms or shared between atoms. By this mechanism, atoms are able to bond into molecules and other types of chemical compounds like ionic and covalent network crystals.

Sources: Wikipedia

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