Awal Mula Satuan

Sejarah satuan panjang

Berbicara mengenai besaran-besaran fisis, pasti akan melibatkan sebuah angka dalam sebuah pengukuran dengan satuan dari besaran fisis tersebut. Namun akan ada beberapa pertanyaan dalam benak kita mengenai angka dari suatu pengukuran dalam besaran fisis, “seberapa panjang untuk tiap meter itu?”  Apakah satuan meter hanya ratusan kali dari satuan senti dan ribuan bagian dari kilometer, tentu itu sebuah pendapat yang sangat sempit. Jika kita menelaah lebih jauh dan luas dari sebuah penemuan satuan panjang akan sangat susah bagi kita untuk mendefinisikan satuan panjang itu sendiri waktu itu sebab belum ada sebuah parameter yang menjelaskan dengan rinci seberapa jauhkan untuk niai satu meter tersebut. Mari kita simak sejarah dari satuan panjang.

Mula-mula satu meter didefinisikan berdasarkan keliling bumi. Ditetapkan bahwa keliling  garis bujur  bumi yang melalui kota Paris, Prancis ditetapkan memiliki panjang 40.000.000 m  . Jadi panjang satu meter sama dengan 1/40.000.000 keliling garis bujur bumi yang melalui kota Paris. Definisi ini menjadi tidak memadai ketika perkembangan ilmu pengetahuan dan teknologi menuntut pengukuran yang makin akurat. Tidak mungkin pengukuran yang akurat diperoleh dari satuan standar yang tidak akurat.

Pada akhir abad ke-19, panjang satu meter didefinisikan ulang. Panjang satu meter ditetapkan sama dengan jarak dua goresan pada batang campuran logam platina dan iridium yang tersimpan di International Bureau of Weight and Measures  di kota Sevres, Prancis  . Logam tersebut disimpan pada kondisi yang dikontrol secara ketat utuk menghindari perubahan  dimensi  akibat perubahan kondisi lingkungan seperti suhu, kelembaban udara, tekanan udara, intensitas cahaya, reaksi kimia, dan sebagainya.

Kemudian, Setelah laju cahaya dapat diukur dengan sangat teliti, pada Konferensi Umum Tentang Berat dan Pengukuran ke -17 tahun 1983, panjang satu meter didefinisikan ulang sebagai jarak tempuh cahaya dalam ruang hampa selama 1/299.792.458 sekon. Ini berarti pula bahwa selama satu sekon cahaya merambat dalam ruang hampa sepanjang 299.792.458 meter. Sampai saat ini pengukuran 1 meter masih menggunakan data dari pengukuran dengan cahaya.

Nah sekarang sudah jelas kan Bagaimana susahnya seorang kelompok ilmuwan dalam mendefinisikan sebuah besaran hingga benar-benar mutlak nilainnya. Mungkin saja nilai satu meter yang kita ukur masih bisa berubah seiring Perkembangan zaman yang semakin maju, bisa saja nanti ada parameter-parameter yang lebih akurat dalam pengukuran satuan panang itu sendiri. Sekian dan terima kasih. 

Sumber: Mikrajuddin Abdullah-Fisika Dasar I.

SainsMe – Orang sering bertanya, bagaimana air hujan bisa membuat jalanan aspal yang keras itu hancur dan berlubang-lubang. Jawabannya adalah, karena air bersifat melarutkan.
Ya, hampir semua materi bisa larut dalam air. Dalam bahasa Inggris ada sebuah ungkapan, yang kira-kira begini artinya; “Berikan sedikit waktu, maka air akan melarutkan hampir segalanya”.
Hal ini juga berlaku bagi aspal. Sebelum bicara lebih jauh, ada baiknya kita tahu dulu komponen penyusun jalanan aspal yang keras itu. Pada dasarnya, aspal hanyalah berfungsi sebagai perekat.
Konstruksi jalan tersusun dari batu kerikil, pasir dan bahan-bahan agregat, kemudian semua materi tadi direkatkan oleh semen aspal. Aspal sendiri (atau disebut juga bitumen) adalah bahan hasil tambang, bisa digolongkan dalam minyak bumi (petroleum) yang bersifat lengket, hitam, dan kental. Kita pun harus bangga, sebab salah satu tambang aspal terbesar di dunia ada di pulau Buton, di ujung Sulawesi.
Jika air menggenang dalam waktu yang lama di jalan aspal, maka sedikit demi sedikit aspal di jalan tersebut akan larut! Ya, air akan memecah molekul aspal ke bentuk yang lebih kecil lagi sehingga daya rekatnya menjadi berkurang. Jika kamu mulai melihat banyak batu kerikil yang terlepas di jalan beraspal, itu adalah tanda-tanda awal mulai rusaknya struktur jalan tersebut.
Sebenarnya genangan air saja bukan merupakan masalah besar. Kerusakan menjadi parah karena saat terjadi proses pelarutan aspal, jalan tersebut dilewati oleh kendaraan yang berat. Sehingga struktur jalan yang sedang dalam keadaan lemah tidak kuat menahan beban di atasnya, dan berakhir dengan banyaknya lubang di jalanan.
Perlu diketahui, bahwa idealnya jalanan beraspal sebaiknya didesain dengan bentuk “punggung sapi”. Artinya, bagian tengah harus sedikit lebih tinggi dibanding bagian pinggir jalan, sehingga air tidak akan tergenang dan langsung mengalir.
Demikian pula di tepian jalan, kondisi ideal mengharuskan dibuat saluran air atau parit kecil sehingga air segera pergi dan tak sempat diam dalam waktu yang lama.
Nah, sekarang sudah tahu kan, mengapa setiap habis hujan deras banyak lubang di jalanan. Oh ya satu lagi, terkadang penyebab utamanya adalah komposisi material yang kurang tepat. Terlalu banyak batu kerikil dan pasir, serta terlalu sedikit semen aspal sebagai perekat juga bisa menjadi penyebab jalan aspal cepat rusak lho.
Sumber : Sains.me

Mind Control

How scientists use light to manipulate the brain—and treat illness

A mouse crouches on the ground of atiny low rectangular enclosure. It sniffs the air curiously. Then, atiny low light-weight hooked up to the highest of its head glows blue. The mouse begins running round the enclosure. the sunshine turns off. The mouse stops. By flipping a switch, scientists square measure dominant the a part of the mouse’s brain that creates it run.

A breakthrough technology referred to as optogenetics created this experiment potential back in 2007. Optogenetics lets scientists modify neurons, or brain cells, to form them answer light-weight. They shine light-weight on the cells to activate them. Since some neurons have totally different roles than others, targeting a selected cluster of neurons lets scientists management specific behaviors. “If we tend to wished to, we tend to might produce a mouse that we tend to might run sort of a device automobile,” says Eric Turner, a neurobiologist at city Children’s research facility in Washington.

But Turner and different scientists learning optogenetics have larger ideas. They’re victimization it to know however the brain creates our thoughts, emotions, and behaviors—and the way to treat devastating brain disorders.

BRAIN BASICS

How the brain works is essentially a mystery, even to doctors and scientists. The human brain contains concerning eighty six billion neurons. Electrical signals whiz throughout the brain on pathways that connect multiple neurons, inflicting each behavior from tasting to texting, and each feeling from happiness to worry. working out the one network of neurons that controls every of those responses isn’t straightforward.

Optogenetics is that the 1st tool that might reveal these secrets. Using it, scientists could finally be able to make out what causes psychiatrical disorders like depression and anxiety and diseases like Parkinson’s and brain disorder. higher therapies might then be developed to treat these sicknesses.

A BRIGHT plan

Optogenetics all began with Associate in Nursing unlikely source: chlorophyte. In 2004, Karl Deisseroth, a neurobiologist at Stanford University in Calif., became fascinated by a algae referred to as genus Chlamydomonas. The alga don’t have brains, however they are doing have proteins referred to as opsins. Opsins square measure sensitive to light: once the sun hits one, it sends a blast of electricity through the alga that signals it to maneuver toward or faraway from the sunshine. genus Chlamydomonas uses daylight to form energy, like what plants do throughout chemical action. Moving toward the sun permits them to gather a lot of energy.

Deisseroth puzzled if he might use opsins to “talk” to neurons within the brain. He thought that it would be potential as a result of each opsins and neurons use a similar language: electricity. If he inserted Associate in Nursing protein into a nerve cell, he could be able to modification however the nerve cell behaves by exposing it to light-weight.

No somebody had tried it before as a result of nobody thought it absolutely was potential. “I thought it in all probability wouldn’t work absolutely,” Deisseroth says. “But it absolutely was value a trial.” In 2006, Deisseroth and his team tested their plan on a mouse. They inserted the opsin’s gene—the opsin’s hereditary material—into neurons that management sleep and wakefulness. Then they place a skinny fibreoptic cable into that space of the brain. The cable was connected to a really little optical device, permitting it to shine light-weight directly into the brain.

The team tried the experiment on a sleeping mouse. after they turned on the optical device, the mouse began to maneuver. the sunshine within its head was activating the neurons that tell the mouse, “Wake up!” The experiment was a hit.

MIND MAPPING

Optogenetics is currently one in all the fastest-developing fields in science. By inserting the protein cistron into totally different neurons and flipping on light-weight to check what the mice do, scientists will make out what totally different neural pathways square measure dominant. “You name it—any behavior, any cognition—you will study it with optogenetics,” says Deisseroth.

By bit by bit operating through the brain one neural pathway at a time, scientists hope to form the primary finely elaborate map of the human brain. It might show U.S. however emotions, behaviors, and brain disorders return to be.

HEALING WITH light-weight

One disorder that might enjoy optogenetics is epilepsy—an incurable condition which will cause seizures (uncontrollable shaking of muscles). Epileptic seizures happen once neurons go haywire, firing their electrical signals out of management.

To regulate some severe cases of brain disorder, doctors implant electrodes within the a part of the brain that’s defective. The electrodes emit pulses of electricity that stop the neurons from firing wildly. however electrodes aren’t precise—they will zap healthy neurons along side misfiring ones. With optogenetics, doctors might treat solely the neurons that square measure defective.

People who suffer from anxiety might conjointly profit. Current medicines expose the whole brain to a treatment, which may cause undesirable aspect effects like somnolence or confusion. therefore Deisseroth’s work determined to do to find the precise neurons concerned in anxiety. They place the protein cistron into a circuit of neurons in a very mouse’s basal ganglion, a district of the brain related to worry and anxiety. Then they constituted a cable into the basal ganglion and watched what happened after they flipped the sunshine on (see illustration, right).

Mice square measure petrified of open areas, wherever they can’t hide from predators. once Deisseroth’s team placed the mouse in a very maze, it spent most of its time in a vicinity protected by high walls, sometimes gesture its scent out to explore. however after they switched on the sunshine, the mouse suddenly ventured out, exploring the open areas without worrying.

The results recommend that the team situated Associate in Nursing anxiety circuit within the brain. Someday, doctors might facilitate individuals with anxiety disorders by treating that circuit with a lot of precise medication.

TOO MUCH CONTROL?

Optogenetics might facilitate several individuals. however is manipulating the brain ethical? Some individuals worry that if scientists will management the brains of mice with light-weight, what’s to prevent somebody from dominant people’s brains against their will?

Deisseroth says current optogenetic technology isn’t nearly refined enough to form this an overseas chance. Plus, he says, the advantages so much outweigh any issues. The potential rewards square measure great: Optogenetics could also be the key to the primary refined treatments for devastating brain disorders. It might conjointly facilitate answer one in all the largest queries of all: however our brains create U.S. World Health Organization we tend to square measure.

HOW TO management A MOUSE’S MIND

Deisseroth’s work used optogenetics to shut off neurons in a very mouse’s brain that cause anxiety. Mice square measure fearful of open areas, however optogenetics will create them live through that worry. the method below shows however it works. Steps two through four show the fundamentals of all optogenetics experiments.

1. Associate in Nursing untreated mouse lingers within the corner of the maze, too afraid to explore on the far side the protected  walls.

2. The protein cistron (the opsin’s hereditary material) is far from photosensitive alga.

3. The protein cistron is inserted into a harmless virus and injected into the brain of a mouse.

4. Neurons, during this case associated with a mouse’s worry response, become conscious of light-weight. 5. Scientists shine light-weight into the mouse’s brain through a cable. The neurons answer light-weight, stopping the mouse’s worry response.


6. The mouse, not fearful of open areas, courageously explores the maze. The animal doesn't expertise anxiety.

Electrical control of quantum bits in silicon paves the way to large quantum computers

Lead man of science, UNSW prof Andrea Morello from the varsity of engineering and Telecommunications, aforesaid his team had with success accomplished a replacement management technique for future quantum computers.
The findings were revealed nowadays within the open-access journal Science Advances.
Unlike typical computers that store knowledge on transistors and laborious drives, quantum computers encipher knowledge within the quantum states of microscopic objects known as qubits.
The UNSW team, that is related  with the ARC Centre of Excellence for Quantum Computation & Communication Technology, was initial within the world to demonstrate single-atom spin qubits in Si, reportable in Nature in 2012 and 2013.
The team has already improved the management of those qubits to associate degree accuracy of higher than ninety nine and established the globe record for the way long quantum data will be keep within the solid state, as revealed in Nature technology in 2014.
It has currently incontestable  a key step that had remained elusive since 1998.
"We incontestable  that a extremely coherent qubit, just like the spin of one phosphorus atom in isotopically enriched Si, will be controlled exploitation electrical fields, rather than exploitation pulses of oscillatory magnetic fields," explained UNSW's Dr Arne Laucht, post-doctoral man of science and lead author of the study.
Associate Professor Morello aforesaid the tactic works by distorting the form of the negatron cloud hooked up to the atom, employing a terribly localized field.
"This distortion at the atomic level has the result of modifying the frequency at that the negatron responds.
"Therefore, we are able to by selection opt for that qubit to control. it is a bit like choosing that station we tend to tune to, by turning a straightforward knob. Here, the 'knob' is that the voltage applied to alittle conductor placed higher than the atom."
The findings recommend that it might be attainable to domestically management individual qubits with electrical fields in a very large-scale quantum laptop exploitation solely cheap voltage generators, instead of the big-ticket high-frequency microwave sources.
Moreover, this specific style of quantum bit will be factory-made employing a similar technology to it utilized for the assembly of everyday computers, drastically reducing the time and value of development.
The device employed in this experiment was invented at the Naval Special Warfare node of the Australian National Fabrication Facility, together with the cluster crystal rectifier by UNSW Scientia prof Apostle Dzurak.
Key to the success of this electrical management technique is that the placement of the qubits within a skinny layer of specially sublimate Si, containing solely the silicon-28 atom.
"This atom is utterly non-magnetic and, not like those in present Si, doesn't disturb the quantum bit," prof Morello aforesaid.
The sublimate Si was provided through collaboration with prof Kohei Itoh from Keio University in Japan.

MAGNETIC FIELD

MAGNETIC FIELD

Flux Lines. within the area around each magnet there exists a magnetic flux. (A magnetic flux is associate example of the natural phenomenon referred to as a field; another samples of a force field ar the electrical field around each electrical phenomenon and also the force field around each mass.) A magnetic flux will be visualised as consisting of lines of attractive force, or flux, originating at a pole and ending at a South Pole. This direction, from the north to the South Pole, is outlined because the direction of the magnetic flux.

Flux lines haven't any material existence; they're just a convenient thanks to visualize a magnetic flux. However, they will be incontestible physically. a way to try to to this can be to position a sheet of paper over a magnet and sprinkle iron filings on the paper. The iron filings can align themselves on flux lines and convey out the pattern of the magnetic flux. (Jiggling or sound the paper helps to bring out the pattern.) Another technique is to position little compasses at numerous points around a magnet. The compass needle aligns itself on a line of force. If the orientation of the needle is recorded at several locations, the pattern of the sphere can emerge.

Flux lines ne'er cross each other, and that they behave as if subject to 2 competitory forces: every line tries to shrink to the tiniest attainable length, however it's conjointly repelled by the neighboring lines. Thus, a north and a South Pole attract one another as a result of the lines between them try and shrink. within the case of like poles, the lines don't connect one pole to the opposite, and also the poles ar pushed apart as a result of every line is repelled by the neighboring lines and tries to place the maximum amount area as attainable between itself and its neighbors. Here again, it ought to be emphasised that the lines ar just a convenient model.

The strength of a magnetic flux refers to the force that a magnet, a bit of iron, or another check object feels at a specific purpose within the field. Strength is proportional to the concentration of the flux lines. wherever the lines ar targeted (close together), as within the region close to a pole, the sphere is strong; wherever the lines ar way apart, the sphere is weak.

Magnetic-field strength decreases speedily with distance from the magnet. The decrease obeys the inverse sq. law—that is, the strength is proportional to 1/r2, wherever r is that the distance from the magnetic pole. Doubling the space, as an example, reduces the strength to 1 fourth.

Atomic Basis of Magnetism. as a result of matter is created from atoms, and atoms ar charged nuclei enclosed by orbiting electrons, every atom could be a potential magnet. However, the orbital rotation of electrons produces solely a awfully weak magnetic flux. it's the spinning of the electrons as they orbit the atomic nucleus that offers materials magnetic properties. In most substances [*fr1] the orbiting electrons spin in one direction and also the spouse within the reverse direction, thereby canceling any magnetic result. In iron, however, of the fourteen electrons within the third shell (or orbit), the amount of electrons with positive spin doesn't equal the amount of electrons with negative spin. This makes every iron atom act sort of a little magnet; it possesses a property referred to as torsion. in an exceedingly piece of iron, once the magnetic moments ar all aligned within the same direction, the piece of iron as an entire becomes magnetic. This behavior of iron is named magnetism. Iron, nickel, and cobalt, among the alleged transition parts, and a number of other of the rare-earth parts (atomic numbers fifty seven through 71) ar labeled  magnetism as a result of they share iron's magnetic property. as a result of iron displays the strongest magnetism and is lowest in value, it's most typically wont to create magnets. (Several of the rare-earth parts become a lot of powerfully magnetic than iron below temperature.)

Not all iron bars ar magnets. The "atomic magnets," created by a web negatron spin, should be aligned so a majority of them ar orientating in an exceedingly explicit direction. Otherwise the atomic magnets can cancel one another, and also the bar won't be a magnet.

Magnetic properties ar full of temperature. the upper the temperature, the less magnetism there'll be in an exceedingly magnet, till all magnetization disappears at what's referred to as the temperature, or Curie point. The temperature is concerning 770° C (1420° F) for iron, 1120° C (2050° F) for metal, and 358° C (676° F) for nickel. (When a magnet cools, it once more becomes ferromagnetic; but, if it's a static magnet, it's to be remagnetized.)

Electricity and Magnetism. electrical and magnetic phenomena ar intimately connected. One cannot exist while not the opposite, and also the 2 sets of phenomena ar typically referred to as electromagnetism. as an example, each moving electrical phenomenon produces a magnetic flux around itself. as a result of an electrical current could be a flow of electrical charges, a current-carrying wire includes a magnetic flux around it. The magnetic flux lines of this field ar closed loops close the wire. Physicists have long used the "right-hand rule" to recollect the direction of this magnetic flux. Hold the proper hand within the hitchhiker's position: once the thumb points within the direction of the electrical current, the other, curled fingers can purpose within the direction of the magnetic flux. (We ar mistreatment the traditional definition of the direction of an electrical current: the direction is opposite to the direction during which the electrons ar flowing through the wire. an electrical current outlined during this manner typically is just referred to as an electrical current, or typically a standard current; an electrical current outlined as flowing within the same direction because the negatrons is named associate electron current.)

If a current-carrying wire is bent into a loop, the flux lines all bear the loop within the same direction; as a result a magnet is created. The magnet will be created abundant stronger if we tend to bend the wire into several loops—that is, into a spiral or coil—so that there's a bigger concentration of flux lines rummaging the coil. as a result of flux lines choose to bear iron instead of air or empty area, we will concentrate the lines even a lot of by inserting associate iron core into the coil. What we've got now's associate magnet. the nice advantage of associate magnet is that the sphere it creates will be turned on and off by turning this on and off. conjointly the magnetic flux (or poles) will be reversed by reversing the flow of current within the coil.

Magnetic Interactions. A magnet attracts associate unmagnetized piece of iron by turning it into a magnet briefly. as an example, once a magnet is brought close to associate iron or steel staple, the magnetic flux from the static magnet aligns a number of the atomic magnets within the staple, thereby inflicting the staple to become a brief magnet. This briefly magnetic  staple has its South Pole attracted (by manner of its magnetic field) to the pole of the static magnet, and also the staple attaches itself to the magnet. The staple, currently a magnet, will attract alternative paper clips within the same manner. once the staple is aloof from the magnetic flux, its atoms lose their alignment, and also the steel becomes demagnetized.

When electrons ar in motion, they produce a magnetic flux. Therefore, if associate negatron moves through a magnetic flux, the sphere created by the moving negatron can act with the magnetic flux that the negatron is moving through, and also the negatron are going to be deflected from its initial course. Physicists use a "left-hand rule" to indicate the interaction of those forces. The forefinger points within the direction of the magnetic flux (going from north to south); the center finger points within the direction of a positive particle's movement (or the direction from that a negative particle is moving); and also the thumb indicates the direction of the force to that the particle are going to be subjected. the ultimate direction of the particle is decided by the vector of speed|the speed|the rate} imparted by this force and also the initial velocity of the particle coming into the magnetic flux. This deflection of a charged particle (or of a beam of charged particles) is created use of in several devices. In associate microscope, as an example, a beam of electrons traveling on associate exhausted tube is deflected and targeted by magnet "lenses" within the type of coils round the tube. Particle accelerators (atom smashers) use huge magnets to manage the ways of charged particles. tv image tubes, oscilloscopes, and plenty of alternative devices conjointly create use of the deflection of a beam of charged particles by magnetic (and by electric) fields.

A region will be secure from magnetic fields by close it with iron or another magnetic material. The flux lines pass preferentially through the iron and avoid the realm within.