Keajaiban Rancangan pada Kemampuan Terbang Serangga

Jika masalah penerbangan direnungkan, burung segera terlintas dalam pikiran. Namun, burung bukanlah satu-satunya makhluk yang dapat terbang. Beberapa jenis serangga juga dilengkapi dengan kemampuan terbang yang melebihi kemampuan burung. Kupu-kupu Raja dapat terbang dari Amerika Utara hingga ke pedalaman Benua Amerika. Lalat dan capung bahkan dapat tetap diam di udara.

Para evolusionis menyatakan bahwa serangga mulai terbang sejak 300 juta tahun yang lalu. Meski demikian, mereka tidak mampu memberikan jawaban tuntas terhadap pertanyaan-pertanyaan mendasar seperti: bagaimana caranya serangga pertama membentuk sayap-sayapnya, memulai terbang, dan bisa diam di udara?

Evolusionis hanya menyatakan bahwa beberapa lapis kulit tubuhnya mungkin telah berubah menjadi sayap. Sadar akan tidak meyakinkannya pernyataan mereka, mereka juga menyatakan bahwa contoh bentuk-bentuk fosil yang menguatkan penilaian ini tidak tersedia lagi.

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Patung Manusia Tertua Punya Payudara Menonjol

BERLIN, KOMPAS.com - Sebuah ukiran gading berbentuk perempuan gendut yang ditemukan di Gua Hohle Fels, Jerman ini punya keunikan. Selain sosoknya yang mengundang perhatian, patung tersebut umurnya sudah sangat tua. Apalagi dibuat dari gading mammoth.

"Ini merupakan ukiran berbentuk sosok manusia yang paling tua di dunia," ujar Jill Cook, seorang kurator paleolitikum dan mesolitikum di British Museum, London. Berdasarkan pengukuran karbon, usianya diperkirakan 35.000 tahun.

Patung-patung baru di Israel dan Afrika sebenarnya ada dua kali lebih tua daripada patung ukiran ini. Namun, bukan hasil pahatan melainkan kumpulan batu yang membentuk sosok manusia.

Saat ditemukan, ukiran gading tersebut telah pecah dalam enam bagian. Hasil rekonstruksi menunjukkan sosok tubuh perempuan tanpa kepala, dengan perut berlemak, payudara menonjol, dan paha besar. Bagian lengannya kirinya hilang.

"Ini sangat berkaitan dengan hal berbau seksual," ujar Nicholas Conard, arkeolog dari Universitas Tuebingen. Menurutnya adanya ukiran berbentuk tubuh manusia ini menunjukkan bahwa manusia sejak lama sudah punya kemampuan menyimbolkan tubuhnya dalam bentuk benda.

Patung ukiran gading ini hanya setinggi 6 centimeter. Conard menduga ukiran tersebut digantung di ujung tali. Namun, fungsinya buat apa tak diketahui pasti meski diperkirakan pembuatnya terobsesi dengan seks.

Secara umum, ukiran ini mirip patung-patung disebut para arkeolog sebagai figur Venus yang khas tanpa kepala dan kaki. Sekitar 150 figur Venus ditemukan antara Pegunungan Pyrenees hingga Russia bagian selatan dan berumur antara 25.000-29.000 tahun.

WAH 
Sumber : AP

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Are Selenium Levels Linked to Diabetes?

Americans with diabetes have high levels of selenium in their bodies, prompting some health experts to suspect that it could contribute to development of the disease. In response to their new findings, a research team has recommended that U.S. residents stop taking supplements that contain selenium. 
 
Most Americans ingest large amounts of the mineral—substantially more than people elsewhere—because soil in much of the country contains high levels that are absorbed by crops. Selenium occurs naturally in soil and leaches onto farm fields from irrigation and streams.

The research team, led by Johns Hopkins University epidemiologists, examined the diabetes rate and selenium levels of 917 people over the age of 40 who participated in a national health study conducted by the U.S. Centers for Disease Control and Prevention in 2003 and 2004. They found that most had a lot of selenium in their blood, but those with diabetes had substantially more.

The benefits and dangers of selenium have been debated in recent years because some studies show it might help protect people from cancer and heart disease. Selenium is an essential element and antioxidant, but medical experts say there is a fine line between the amount that the body needs and the amount that is harmful.

“Given the current diabetes epidemic, the high selenium intake from naturally occurring selenium in U.S. soil and the popularity of multivitamin/mineral supplements containing selenium in the U.S., these findings call for a thorough evaluation of the risk and benefits associated with high selenium status in the U.S.,” the researchers wrote in a study published online in Environmental Health Perspectives on May 15.

“Furthermore,” they wrote, “our findings suggest that selenium supplements should not be used in the U.S. until there is a better understanding of their potential risks and benefits.”

Supplements containing selenium have gained popularity in the United States because of anti-cancer claims, and selenium levels in people have been rising. Nearly one-quarter of Americans over the age of 40 take selenium supplements or multivitamin supplements that include selenium.

Source :http://www.scientificamerican.com/article.cfm?id=selenium-linked-to-diabetes

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Material Kaca Berkarakter Ganda : Cermin dan Transparan

Pada tahun 1996, sekelompok peneliti di Belanda menemukan sejenis material yang dapat di ubah-ubah dari keadaan transparan ke reflektif (cermin) dan atau sebaliknya dengan mengekspos material termaksud dalam gas hidrogen. Peneliti menemukan bahwa film tipis dari metal yang dinamakan yttrium dan lanthanum , dengan bantuan hidrogen, kemudian membentuk senyawa hidrida metalik yang bersifat mengkilap. Jika ditambah lebih banyak lagi hidrogen ia menjadi transparan. Transformasi dari transparan ke reflektif (cermin) dapat dilakukan dengan memompa hidrogen diatas film pada tekanan yang berbeda.

Agar perubahan dari kaca transparan ke cermin dapat dilakukan dengan baik maka peralatannya perlu dioperasikan secara elektris, dan komponen materialnya harus berbentuk benda padat.

Rob Armitage dan rekan-rekannya dari the Lawrence Berkeley National Laboratory, di California, AS menjelaskan cara kerja alat yang dioperasikan dengan tombol . Cermin terdiri dari enam lapisan yang kompleks dan tersimpan pada gelas atau kaca. Lapisan tersebut merupakan logam campuran magnesium dan gadolinium, yang yang dapat bersifat reflektif apabila mengandung sedikit atau tanpa hidrogen tetapi akan menjadi transparan dengan kandungan hidrogen yang tinggi.

Atom hidrogen yang mempengaruhi fase transisi atau fase pergantian dari transparan ke cermin tersebut diatas disimpan dalam lapisan tungsten trioxide yang memiliki muatan positif . Jika lapisan magnesium-gadolinium diberi muatan relatif negatif; terhadap film tungsten trioxide, hidrogen didorong kedalam logam campuran, dan akan menjadi terang. Pada waktu yang bersamaan tungsten trioxide , yang berwarna biru, pudar warnanya ketika hidrogen terbuang. Diantara dua lapisan terdapat ; film tipis palladium yang dapat ditembus oleh hidrogen dan dapat membantu mentransformasikan atom hidrogen bermuatan positif kedalam salah status yang netral , sehingga dapat dikombinasikan dengan logam campuran pada saat membentuk senyawa hidrida. Pada saat voltase atau tegangan berbalik, hidrogen kembali ke lapisan tungsten trioxide, dan logam campuran berubah menjadi cermin kembali.

Para peneliti mengatakan bahwa cermin benda padat yang diuraikan tersebut diatas dapat stabil dalam keadaan transparan untuk beberapa jam. Secara prinsip film logam campuran dapat berubah dari transparan ke cermin hanya dalam beberapa menit saja sehingga cukup prospektif untuk diterapkan.

Cermin dengan tombol listrik serupa di atas mungkin akan berguna bagi teknologi komunikasi optik. Sebagai contoh, pancaran cahaya yang memuat informasi data tertulis dalam pulsa optikal mungkin dapat disalurkan atau dialirkan kembali dari satu serat optik ke serat yang lainnya dengan mentransformasikan kaca jendela transparan ke kaca jendela yang dapat bersifat reflektif serupa cermin.

Referensi: chem-is-try.org

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Unlikely Suns Reveal Improbable Planets

Key Concepts
Few if any astronomers expected the sheer diversity of planets beyond our solar system. The most extreme systems are those that orbit neutron stars, white dwarfs and brown dwarfs.
Neutron stars are born in supernova explosions, and planets orbiting them probably congealed from the debris. The bodies orbiting white dwarfs are the hardy survivors of the demise of a sunlike star. And brown dwarfs, themselves barely more massive than planets, nonetheless appear to be sites of planet formation.

Among the most poignant sights in the heavens are white dwarfs. Although they have a mass comparable to our sun’s, they are among the dimmest of all stars and becoming ever dimmer; they do not follow the usual pattern relating stellar mass to brightness. Astronomers think white dwarfs must not be stars so much as the corpses of stars. Each white dwarf was once much like our sun and shone with the same brilliance. But then it began to run out of fuel and entered its stormy death throes, swelling to 100 times its previous size and brightening 10,000-fold, before shedding its outer layers and shriveling to a glowing cinder the size of Earth. For the rest of eternity, it will sit inertly, slowly fading to blackness.

As if this story were not gloomy enough, it gets worse. We and our colleagues have found more than a dozen white dwarfs in our galaxy that are orbited by asteroids, comets and perhaps even planets—entire graveyards of worlds. While the stars were still alive, they rose every day in the skies of these worlds. They gently warmed the soil and stirred the wind. Living organisms may have soaked up their rays. But when the stars died, they vaporized or engulfed and incinerated their inner planets, leaving only the bodies that resided in the chilly outposts. Over time the dwarfs shredded and consumed many of the survivors as well. These decimated systems offer a grim look at the fate of our own solar system when the sun dies five billion years from now.

Astronomers have always suspected that planets might orbit stars other than our sun. We imagined, though, that we would find systems much like our own solar system, centered on a star much like the sun. Yet when a flood of discoveries began 15 years ago, it was apparent right away that extrasolar planetary systems can differ dramatically from our solar system. The first example was the sunlike star 51 Pegasi, found to have a planet more massive than Jupiter on an orbit smaller than that of Mercury. As instruments became more sensitive, they found ever stranger instances. The sunlike star HD 40307 hosts three planets with masses between four and 10 Earth masses, all on orbits less than half the size of Mercury’s. The sunlike star 55 Cancri A has no fewer than five planets, with masses ranging from 10 and 1,000 Earth masses and orbital radii ranging from one tenth that of Mercury to about that of Jupiter. Planetary systems imagined in science fiction scarcely compare.

The white dwarf systems demonstrate that the stars do not even need to be sunlike. Planets and planetary building blocks can orbit bodies that are themselves no larger than planets. The variety of these systems equals that of systems around ordinary stars. Astronomers hardly expected the ubiquity of planetary systems, their hardiness and the apparent universality of the processes by which they form. Solar systems like our own might not be the most common sites for planets, or even life, in the universe.

Phoenix from the Ashes
It is sometimes forgotten today, but the first confirmed discovery of any extrasolar planets was around a very unsunlike star: the neutron star PSR 1257+12, an even more extreme type of stellar corpse than a white dwarf. It packs a mass greater than the sun’s into the size of a small asteroid, some 20 kilometers across. The event that created this beast, the supernova explosion of a star 20 times the mass of the sun, was more violent than the demise of a sunlike star, and it is hard to imagine planets surviving it. Moreover, the star that exploded probably had a radius larger than 1 AU (astronomical unit, the Earth-sun distance), which is larger than the orbits of the planets we see today. For both reasons, those planets must have risen up out of the ashes of the explosion.

Although supernovae typically eject most of their debris into interstellar space, a small amount remains gravitationally bound and falls back to form a swirling disk around the stellar remnant. Disks are the birthing grounds of planets. Astronomers think our solar system took shape when an amorphous interstellar cloud of dust and gas collapsed under its own weight. The conservation of angular momentum, or spin, kept some of the material from simply falling all the way to the newborn sun; instead it settled into a pancake shape. Within this disk, dust and gas coagulated into planets [see “The Genesis of Planets,” by Douglas N. C. Lin; Scientific American, May 2008]. Much the same process could have occurred in the postsupernova fallback disk.

Source:

http://www.scientificamerican.com/article.cfm?id=improbable-planets

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