國際科技信息

“生物支架”可修復先天性心臟缺損

近日，美國萊斯大學和德州兒童醫(yī)院的研究人員成功制成了一種名為“生物支架”的生物相容性補丁，能夠修復嬰兒的先天性心臟缺損。其能與活性心肌細胞相容，并可支撐新的健康組織的生長。隨時間推移，它也會逐漸降解。相關(guān)研究報告發(fā)表在近期出版的《生物材料學報》上。

一個好的支架需能夠完美地執(zhí)行多種功能：它需要強大到足以承受心臟跳動的壓力，還能良好地擴展和收縮。另外還需要具有孔洞支持新的心臟細胞的遷移，使它們自發(fā)建立連接，形成自然支架以取代植入的補丁。同時其還要足夠堅韌以支持縫合過程，并能在自然組織發(fā)揮作用后適時進行生物降解。

目前用于治療先天性心臟缺損的修復補丁多由合成纖維制成，或取材自乳牛或病患本體。但這種補丁并不具有活性，其就如塑料一般，無法與病患的心臟組織融為一體，并具有引發(fā)心力衰竭、心律失常和纖維性顫動等癥狀的風險。

此次制成的三明治結(jié)構(gòu)支架的中間一層為聚己內(nèi)酯（PCL）聚合物，其能逐漸硬化形成拉伸帶。而混合兩種具有不同分子質(zhì)量的PCL，可在粗糙表面形成微小的孔隙。外面的兩層則是由明膠和脫乙酰殼多糖一比一混合而成的水性凝膠，兩種原材料都很常見。

心肌細胞能在水性凝膠表面增殖，逐漸形成網(wǎng)絡，并能契合心臟組織的舒張和收縮。雖然細胞不能穿過PCL的孔洞，但這些孔隙卻能使營養(yǎng)物質(zhì)從一側(cè)傳輸至另一側(cè)，它們也能使凝膠緊緊附著在PCL的核心。

研究人員在水中測試了PCL的生物降解特質(zhì)。50天后，約有15%的P C L分散開來，形成了不規(guī)則的薄片。他們表示如果PCL被植入人體內(nèi)，這一降解速度將會變慢，需要數(shù)月才能完成。但這個過程也很穩(wěn)定，可支持肌肉組織的逐步構(gòu)建?？茖W家稱，他們希望未來“生物支架”能夠與干細胞衍生的心臟細胞相結(jié)合，在植入嬰兒體內(nèi)后，快速縫合心臟缺陷處，緩解心室壓力，并在之后觀測時表現(xiàn)得與正常組織無異。研究人員還透露，干細胞的可能來源包括羊水和新生兒母體等，這將確保心臟補丁的基因一致性，他們目前亦在進行相關(guān)的研究。下一步，科研人員還將進行數(shù)年測試，直至這種支架順利進入人體試驗階段。

New biocompatible patch can repair congenital heart defects

A painstaking effort to create a biocompatible patch to heal infant hearts is paying off at Rice University and Texas Children's Hospital.

The proof is in a petri dish in Jeffrey Jacot's lab, where a small slab of gelatinous material beats with the rhythm of a living heart.

Jacot, lead author Seokwon Pok, a postdoctoral researcher at Rice, and their tissue-engineering colleagues have published the results ofyears of effort to produce a material called a bioscaffold that could be sutured into the hearts of infants suffering from birth defects. The scaffold, seeded with living cardiac cells, is designed to support the growth of healthy new tissue. Over time, it would degrade and leave a repaired heart.

The research was detailed in the Elsevier journal Acta Biomaterialia.

Patches used now to repair congenital heart defects are made of synthetic fabrics or are taken from cows or from the patient's own body. About one in 125 babies born in the United States suffers such a defect; three to six of every 10,000 have what's known as a defect called Tetralogy of Fallot, a cause of "blue baby syndrome" that requires the surgical placement of a patch across the heart's right ventricular outflow tract.

Current strategies work well until the patches, which do not grow with the patient, need to be replaced, said Jacot, an assistant professor of bioengineering at Rice University, director of the Pediatric Cardiac Bioengineering Laboratory at the Congenital Heart Surgery Service at Texas Children's Hospital and an adjunct professor at Baylor College of Medicine.

"None of those patches are alive," Jacot said, including the biologically derived patches that are "more like a plastic" and are not incorporated into the heart tissue.

"They're in a muscular area in the heart that's important for contraction and, more so, for electrical conduction," he said. "Electrical signals have to go around this area of dead tissue. And having dead tissue means the heart produces less force, so it's not surprising that children with these types of repairs are more at risk for developing heart failure, arrhythmias and fibrillation.

"What we're making can replace current patches in an operation that surgeons are already familiar with and that has a very high short- and medium-term success rate, but with long-term complications," he said.

A better scaffold would have to perform many functions perfectly. It must be strong enough to withstand the pressures delivered by a beating heart yet flexible enough to expand and contract; porous enough to allow new heart cells to migrate, make connections and excrete their own natural scaffold to replace the patch; and tough enough to handle sutures but still be able to biodegrade over just the right amount of time for natural tissue to take over.

The sandwich the researchers created seems to fill the bill on all counts. In the middle is a selfassembled polycaprolactone (PCL) polymer that hardens into a tough but stretchable ribbon. Mixing two types of PCL with different molecular weights allows tiny pores to form along the rough surface. The "bread" is a hydrogel made from a 50/50 mixture of gelatin and chitosan, a widely used material made from the shells of crustaceans like shrimp.

Heart cells cultured on the hydrogel surface were able to thrive and formed networks and ultimately beat. Though cells could not attach to the surface or pass through the pores of the PCL, the pores do allow nutrients to migrate from one side to the other, Jacot said. They also allow the hydrogel to hold on to the PCL core.

新熒光成像技術(shù)可清晰呈現(xiàn)血管脈動

美國斯坦福大學的科學家開發(fā)出一種熒光成像技術(shù)，能夠使活體動物血管脈動以前所未有的清晰度呈現(xiàn)。與傳統(tǒng)的影像技術(shù)相比，其增加的清晰度類似于擦拭掉眼鏡前的迷霧一般。該研究結(jié)果發(fā)表在最新一期的《自然醫(yī)學》雜志在線版上。

該技術(shù)被稱為近紅外-Ⅱ成像，或NIR-Ⅱ。研究人員首先將水溶性碳納米管注射到活體的血液中，然后用激光照射要觀察的對象，如小白鼠。

激光的波長在近紅外范圍內(nèi)，約為0.8微米，可導致專門設計的碳納米管發(fā)出1微米至1.4微米的波長更長的熒光，用于檢測確定血管的結(jié)構(gòu)。

碳納米管發(fā)出的熒光波長要比傳統(tǒng)成像技術(shù)更長，這是實現(xiàn)令人驚嘆的微小血管清晰圖像的關(guān)鍵。由于更長波長光散射較少，因此形成了更清晰的血管圖像。

此外，這種技術(shù)使圖像呈現(xiàn)更精致的細節(jié)，允許研究人員能夠獲得一個快速的圖像采集速度，近乎實時地測量血流量。

同時獲得血流信息和看到清晰血管對于動脈疾病動物模型的研究將特別有用，如血流是如何受到動脈阻塞和收縮誘發(fā)的影響，還有其他事項如中風和心臟病發(fā)作的影響。

研究人員說：“對于醫(yī)學研究而言，這是一個非常好的觀察小動物特征的工具。其將有助于我們更好地理解一些血管疾病，以及其對于治療的反應和如何可以設計出更好的治療?！?/p>

由于NIR-Ⅱ至多只能穿透身體1厘米，所以它不會取代其他成像技術(shù)，而是X射線、CT、MRI和激光多普勒技術(shù)的補充。不過，它卻是一個用于研究動物模型的強大方法。

研究人員說，下一步將使這項技術(shù)在人體內(nèi)更容易接受應用，并探索可替代的熒光分子。

他們希望找到小于碳納米管又能夠發(fā)出同樣波長光的物質(zhì)，以便使其可以很容易地從體內(nèi)排出，消除任何毒性的擔憂。

New technique for visualizing blood flow involves carbon nanotubes and lasers

Stanford scientists have developed a fluorescence imaging technique that allows them to view the pulsing blood vessels of living animals with unprecedented clarity. Compared with conventional imaging techniques, the increase in sharpness is akin to wiping fog off your glasses.

The technique, called near infrared-II imaging, or NIR-II, involves first injecting water-soluble carbon nanotubes into the living subject's bloodstream.

The researchers then shine a laser (its light is in the near-infrared range, a wavelength of about 0.8 micron) over the subject; in this case, a mouse.The light causes the specially designed nanotubes to fluoresce at a longer wavelength of 1-1.4 microns, which is then detected to determine the blood vessels' structure.

That the nanotubes fluoresce at substantially longer wavelengths than conventional imaging techniques is critical in achieving the stunningly clear images of the tiny blood vessels: longer wavelength light scatters less, and thus creates sharper images of the vessels. Another benefit of detecting such long wavelength light is that the detector registers less background noise since the body does not does not produce autofluorescence in this wavelength range.

In addition to providing fine details, the technique - developed by Stanford scientists Hongjie Dai, professor of chemistry; John Cooke, professor of cardiovascular medicine; and Ngan Huang, acting assistant professor of cardiothoracic surgery - has a fast image acquisition rate, allowing researchers to measure blood flow in near real time.

The ability to obtain both blood flow information and blood vessel clarity was not previously possible, and will be particularly useful in studying animal models of arterial disease, such as how blood flow is affected by the arterial blockages and constrictions that cause, among other things, strokes and heart attacks.

"For medical research, it's a very nice tool for looking at features in small animals," Dai said. "It will help us better understand some vasculature diseases and how they respond to therapy, and how we might devise better treatments."

Because NIR-II can only penetrate a centimeter, at most, into the body, it won't replace other imaging techniques for humans, but it will be a powerful method for studying animal models by replacing or complementing X-ray, CT, MRI and laser Doppler techniques.

The next step for the research, and one that will make the technology more easily accepted for use in humans, is to explore alternative fluorescent molecules, Dai said. "We'd like to find something smaller than the carbon nanotubes but that emit light at the same long wavelength, so that they can be easily excreted from the body and we can eliminate any toxicity concerns."

The lead authors of the study are graduate student Guosong Hong of the Department of Chemistry and research assistant Jerry Lee of the School of Medicine. Other co-authors include graduate student Joshua Robinson and postdoctoral scholars Uwe Raaz and Liming Xie. The work was supported by the National Cancer Institute, the National Heart, Lung and Blood Institute and a Stanford Graduate Fellowship.

“三明治”新結(jié)構(gòu)創(chuàng)建出“有來無回”光陷阱

美國普林斯頓大學的研究人員發(fā)現(xiàn)了一種可將有機太陽能電池效率提高近兩倍的新方法?？茖W家們認為，這種廉價的柔性塑料裝置或?qū)⒊蔀樘柲馨l(fā)電的未來。該研究成果將刊登在近期《光學快報》網(wǎng)絡版上。

由普林斯頓大學機電工程系納米結(jié)構(gòu)實驗室主任周郁（音譯）教授領(lǐng)導的研究團隊，通過使用納米結(jié)構(gòu)的金屬和塑料“三明治”來收集和誘捕光線，將有機太陽能電池效率提升了175%。

周教授表示，這項技術(shù)也應能提高傳統(tǒng)的無機太陽能集熱器，如標準的硅太陽能電池板的效率。

導致太陽能電池損失能量的兩個主要問題是：電池的光反射及無法充分捕捉進入電池的光線。

研究團隊的金屬“三明治”新結(jié)構(gòu)——次波長等離子腔可同時解決這兩個問題，其具有抑制反射和捕獲光線的非凡能力。

新電池的頂層（即窗口層）使用極精細金屬網(wǎng)，金屬厚度為30納米，網(wǎng)孔直徑為175納米，間隔為25納米。該金屬網(wǎng)取代了以往由銦—錫—氧化物（ITO）材料制成的窗口層。

該網(wǎng)格狀窗口層與“三明治”結(jié)構(gòu)的底層非常接近，底層使用的是與傳統(tǒng)太陽能電池中相同的金屬膜。兩個金屬板之間夾雜著太陽能電池板中使用的半導體材料薄帶。其可以是硅、塑料或砷化鎵中的任一種。周郁研究團隊使用的是85納米厚的塑料。

太陽能電池的網(wǎng)孔間隔，“三明治”結(jié)構(gòu)厚度乃至網(wǎng)孔直徑，都要小于所收集的光的波長。研究團隊發(fā)現(xiàn)，使用這些次波長結(jié)構(gòu)，使他們能夠創(chuàng)建出一個幾乎“有來無回”的光陷阱。

此項新技術(shù)使研究團隊最終創(chuàng)造出一個僅反射4%光線，即光吸收率高達96%的太陽能電池。在陽光直射情況下，其光電轉(zhuǎn)換效率要比常規(guī)太陽能電池高出52%；在陰天或電池不直接面向太陽，光線以更大角度入射到太陽能板時，該結(jié)構(gòu)可獲得更高的效率。通過捕捉斜射光線，新結(jié)構(gòu)可額外提升81%的效率，從而使最終的效率增長達到了175%。

Tiny structure gives big boost to solar power

Princeton researchers have found a simple and economical way to nearly triple the efficiency of organic solar cells, the cheap and flexible plastic devices that many scientists believe could be the future of solar power.

The researchers, led by electrical engineer Stephen Chou, were able to increase the efficiency of the solar cells 175 percent by using a nanostructured "sandwich" of metal and plastic that collects and traps light. Chou said the technology also should increase the efficiency of conventional inorganic solar collectors, such as standard silicon solar panels, although he cautioned that his team has not yet completed research with inorganic devices.

Chou, the Joseph C. Elgin Professor of Engineering, said the research team used nanotechnology to overcome two primary challenges that cause solar cells to lose energy: light reflecting from the cell, and the inability to fully capture light that enters the cell.

With their new metallic sandwich, the researchers were able to address both problems. The sandwich — called a subwavelength plasmonic cavity — has an extraordinary ability to dampen reflection and trap light. The new technique allowed Chou's team to create a solar cell that only reflects about 4 percent of light and absorbs as much as 96 percent. It demonstrates 52 percent higher efficiency in converting light to electrical energy than a conventional solar cell.

That is for direct sunlight. The structure achieves even more efficiency for light that strikes the solar cell at large angles, which occurs on cloudy days or when the cell is not directly facing the sun. By capturing these angled rays, the new structure boosts efficiency by an additional 81 percent, leading to the 175 percent total increase. Chou said the system is ready for commercial use although, as with any new product, there will be a transition period in moving from the lab to mass production.

The physics behind the innovation is formidably complex. But the device structure, in concept, is fairly simple.

The top layer, known as the window layer, of the new solar cell uses an incredibly fine metal mesh: the metal is 30 nanometers thick, and each hole is 175 nanometers in diameter and 25 nanometers apart. (A nanometer is a billionth of a meter and about one hundredthousandth the width of human hair). This mesh replaces the conventional window layer typically made of a material called indiumtin-oxide (ITO).

The mesh window layer is placed very close to the bottom layer of the sandwich, the same metal film used in conventional solar cells. In between the two metal sheets is a thin strip of semiconducting material used in solar panels. It can be any type — silicon, plastic or gallium arsenide — although Chou's team used an 85-nanometer-thick plastic.

The solar cell's features — the spacing of the mesh, the thickness of the sandwich, the diameter of the holes — are all smaller than the wavelength of the light being collected. This is critical because light behaves in very unusual ways in subwavelength structures. Chou's team discovered that using these subwavelength structures allowed them to create a trap in which light enters, with almost no reflection, and does not leave.

"It is like a black hole for light," Chou said. "It traps it."

The team calls the system a "plasmonic cavity with subwavelength hole array" or PlaCSH. Photos of the surface of the PlaCSH solar cells demonstrate this light-absorbing effect: under sunlight, a standard solar power cell looks tinted in color due to light reflecting from its surface, but the PlaCSH looks deep black because of the extremely low light reflection.

借助基因修改的HIV成功治療一名白血病患者

近日，美國費城兒童醫(yī)院的醫(yī)生宣稱，他們從病魔手中成功奪回了一個罹患白血病的7歲女孩的生命，贏得這場勝利多虧了一個可能會讓所有人感到意外的“幫手”——經(jīng)過基因修改的HIV（人類免疫缺陷病毒）。不過，主治醫(yī)生強調(diào)，治療過程不會出現(xiàn)感染艾滋病的風險。

這個名叫艾米莉的小女孩接受了近兩年的化療，其間病情兩次復發(fā)，醫(yī)生們認為她治愈的“希望渺?！薄?/p>

于是在今年2月，他們開始對她實施這一“以毒攻毒”的實驗性治療方案（官方名稱為CTL019療法）。

醫(yī)生們將HIV中引發(fā)艾滋病的因素剔除，借助這些經(jīng)過基因修改的HIV，艾米莉自己的免疫細胞占據(jù)了優(yōu)勢，一舉擊潰了入侵的白血病細胞。艾米莉是參與CTL019療法的為數(shù)不多的志愿者中唯一的兒童。費城兒童醫(yī)院強調(diào)，該療法還不能被稱為“神奇的子彈”，但至少在艾米莉身上顯示出了巨大的成功。

在治療過程中，醫(yī)生先將艾米莉自己的數(shù)百萬免疫系統(tǒng)細胞移除，接著用經(jīng)過基因修改的HIV將一種能夠增強免疫細胞的新基因送入她體內(nèi)，這種基因如同導彈一樣，可以幫助免疫細胞“鎖定”潛藏起來的白血病細胞并發(fā)動攻擊。

主治醫(yī)生、兒科腫瘤學家斯蒂芬·格拉普說，負責運送新基因的HIV中能夠?qū)е掳滩〉牟糠秩急惶蕹?，因此治療過程中不會出現(xiàn)任何感染艾滋病的風險。

目前艾米莉已經(jīng)回到學校繼續(xù)學習，還能進行遛狗、踢足球等活動。

醫(yī)生表示，艾米莉的治療結(jié)果是“完滿的”，最重要的是，增強了的免疫防護系統(tǒng)仍然“存留在她體內(nèi)，以防止癌癥復發(fā)”。

“任何我們能夠做的檢測，即使是最敏感的測試都表明，她身體里已經(jīng)沒有白血病癥狀了。”格拉普說，“我們還需要觀察幾年看看病情緩解情況，才能考慮她是否已被治愈。目前下斷言還為時尚早。”

格拉普表示，這是他第一次看到治療白血病的標準手段骨髓移植可能有了替代方案，細胞療法有望最終取代昂貴而痛苦的骨髓移植治療。

Doctors ‘cure’ leukemia by using HIV to rewire immune system

Doctors have successfully used a disabled version of HIV to modify a 7-year-old leukemia patient’s white blood cells to attack her cancer. The breakthrough procedure could potentially replace bone marrow transplant as a leukemia treatment.

Emma Whitehead was selected as a patient for the experimental technique after two years of battling with acute lymphoblastic leukemia, the New York Times reported. Chemotherapy failed to either cure the disease or result in a period of remission long enough for a bone marrow transplant.

The process was previously tested only on adult patients. In April, Whitehead became the first child to undergo the treatment, her medical team revealed during an annual meeting of the American Society of Hematology in Atlanta last weekend. She was also the first patient to be treated for her kind of leukemia.

Doctors from the University of Pennsylvania and the Children's Hospital of Philadelphia manipulated Whitehead’s immune system to make it target cancer cells. They took a batch of her own T cells - a kind of white blood cell - and genetically engineered them to kill the B cells - another kind of white blood cell - responsible for her disease.

To do this, the doctors used a modified and disabled form of HIV, the virus responsible for AIDS, to alter the T cells’ genes, making them produce a protein called a chimeric antigen receptor on their surface. This artificial protein matches another protein encountered only on the surface of B cells. The alteration allows T cells to attach to B cells, and destroy them. The genetically engineered T cells were then injected back into Whitehead’s blood, where they could reproduce on their own.

Two months after the procedure, testing revealed there was no sign of cancer in the girl’s body. The altered T cells were still present in her blood, but in smaller quantities than during treatment. Six months later, Whitehead is still in remission and is now back in school.

The experimental treatment has not yet been fully tested: Whitehead nearly died when the procedure caused a spontaneous high fever, and other near-fatal symptoms.

Not all of the 12 patients in the clinical trial responded to the treatment as well as Whitehead: Three adults with chronic leukemia had complete remissions; four improved their condition, but did not beat the disease completely; one is still in too early a stage to evaluate; two patients saw no effect from the treatment; another child initially responded, but eventually relapsed.

The treatment also kills healthy B cells along with malignant ones, making patients vulnerable to certain types of infections; patients require regular treatments of immune globulins to prevent illness.

T cell therapy appears to be a promising medical breakthrough that may replace older bone marrow treatments, the researchers said. They plan to conduct additional trials with at least a half-dozen patients over the next year.

基因發(fā)出“死神預言”:何時死去可以預知

當一個人臨近死亡的時候，如果有人告訴他，你將會在某天的上午或下午死去，這將是一件多么恐怖的事情。

然而，這樣的事情可能就會發(fā)生了，而發(fā)出這樣預言的其實是一種控制人體生理節(jié)律的基因，因為臨近死亡時，人的身體會還原到一種更加自然的生理節(jié)律，這也許就是死神的預言吧。

基因“開關(guān)”決定了我們身體的很多特征，包括頭發(fā)顏色、血型等等，而且對于某些疾病非常敏感?，F(xiàn)在研究人員認為他們已經(jīng)發(fā)現(xiàn)了一種能夠決定更加怪異事情的基因：一個人可能離世的時間。

在發(fā)表于2012年11月《神經(jīng)學年鑒》雜志的一項研究中，研究人體生物鐘(也稱作生理節(jié)律)的科學家們聲稱發(fā)現(xiàn)了基因變體，不僅能夠確定你能否成為一個早起的人，而且也能夠以令人不安的精確度預測出你可能去世的時間。

根據(jù)哈佛醫(yī)學院公布的一份聲明，這種基因可能存在三種核苷酸組合(四種核苷酸構(gòu)建了DNA模塊)：腺嘌呤與腺嘌呤組合(A-A)、腺嘌呤與鳥嘌呤組合(A-G)、鳥嘌呤與鳥嘌呤組合(G-G)。

撒珀爾博士在聲明中寫道：“這種特別的基因類型幾乎影響每個人的睡覺和覺醒模式。而且它擁有一種相當深遠的效果，擁有A-A基因類型的人們比那些擁有G-G基因類型的人們要早起大約1個小時，而A-G類型的人醒來的時間幾乎正好就在中間?！?/p>

此外，研究人員已經(jīng)發(fā)現(xiàn)1200名參與實驗的老年人中有一些人的去世時間與這些核苷酸序列所準確預測的時間相差只有幾個小時。具有A-A和A-G基因類型的病人在上午11點之前去世，而擁有G-G組合的人趨向于下午6點左右去世。

撒珀爾博士說道：“因此真的有一種基因預測你去世的時間。不是日期，而是一天中的時刻。”據(jù)《大西洋月刊》報告，研究人員相信他們的結(jié)果或許是當死亡接近的時候人體會還原到一種更加自然的生理節(jié)律感應階段，而不是生活習慣所產(chǎn)生的循環(huán)。

Gene Predicts Time Of Death Down To Hour, Study Suggests

Genetic "switches" determine much about our bodies, including hair color, blood type, and susceptibility to certain diseases. Now, researchers believe they have found a gene that regulates something far more eerie: the time of day a person is likely to die.

In an study published in the November 2012 issue of the Annals of Neurology scientists studying the body's biological clock (a.k.a. the circadian rhythm) report the discovery of gene variant that not only determines the likelihood of your being a morning person, but also predicts, with unsettling accuracy, your likely time of death.

The gene typically allows for three possible combinations of nucleotides (the four molecular building blocks of DNA): adenineadenine (A-A), adenine-guanine (A-G), and guanine-guanine (G-G), according to a written statement released by Harvard Medical School.

"This particular genotype affects the sleep-wake pattern of virtually everyone walking around," Dr. Clifford Saper, chief of neurology at Beth Israel Deaconess Medical Center in Boston, wrote in the statement. "And it is a fairly profound effect so that the people who have the A-A genotype wake up about an hour earlier than the people who have the G-G genotype, and the A-Gs wake up almost exactly in the middle."

Moreover, investigators realized as some of the 1,200 older subjects in the project died that these nucleotide sequences were accurate predictors of their time of death, within a range of only a few hours.

Patients with the A-A and A-G genotypes typically died just before 11 a.m., while subjects with the G-G combination tended to die near 6 p.m.

"So there is really a gene that predicts the time of day that you’ll die. Not the date, fortunately, but the time of day," said Saper.

The Atlantic reports researchers believe their results may be due to the human body reverting to its more natural, circadian rhythm-induced state as death approaches, instead of the cycle created by social commitments.

零重力下生長氦晶體獲得成功

最近，日本物理學家在研究零重力條件下晶體生長的過程中，突破了實驗室條件限制，在飛機上用氦-4超流液生成了長達10毫米的氦晶體，檢驗了氦晶體在更寬廣條件下生長的特殊動力學，這是普通材料無法實現(xiàn)的。相關(guān)論文發(fā)表在當日的《新物理學雜志》上。

該氦晶體是利用高壓，在0.6K（約零下272℃）的極低溫度下，以超流液潑濺的方式生長出來。超流液是一種量子態(tài)物質(zhì)，其性質(zhì)像液體但黏度為零，所以在高壓下也能暢通無阻。超流液能流過極微小的縫隙而沒有任何摩擦阻力。

晶體生長過程也叫“奧斯特瓦爾德熟化”（Ostwald ripening），即在溶液中，較小的結(jié)晶會溶解并再次沉積到較大的結(jié)晶上?！皧W斯特瓦爾德熟化通常是一種很慢的過程，短時間內(nèi)在較大晶體中幾乎無法看到?！闭撐念I(lǐng)導作者、東京工業(yè)大學教授野村龍司（音譯）說，“對于普通的傳統(tǒng)晶體，要形成最后的固定形狀可能要花幾千年。而低溫氦晶體1秒鐘就能達到它們的最終形狀。一般氦晶體生長超過1毫米時，就會由于重力的作用而變形，這也是我們?yōu)楹我陲w機上做該實驗的原因?！?/p>

當飛機以特殊軌跡，也就是沿拋物線飛行時，飛機上的重力為零。研究人員與日本航空研究開發(fā)機構(gòu)（JAXA）合作，在一架小型噴氣式飛機上進行了實驗。該飛機能提供20秒的零重力條件，在一次兩小時的飛行中，大約能做8個實驗。

他們在飛機上設計了一個專用的小冰箱，上面裝有窗口以觀察晶體形成。他們把一塊較大的氦晶體放在高壓室中，用聲波將其擊碎成微小顆粒，然后潑入氦-4超流液，較小顆粒融解其中，較大的則迅速生長，很快形成一個10毫米長的獨立晶體。

“氦晶體能極快地從超流液中生長出來，因為氦原子是由非常靈敏迅捷的超流液攜帶，結(jié)晶過程不受任何阻礙。這是一種研究晶體形成基本問題的理想材料，因為結(jié)晶速度極快?！饼埶菊f。這項研究有助于人們理解晶體生長背后的基本物理機制，也揭示了隱藏在重力下面的一些現(xiàn)象。

點評

通常情況下，生成氦晶體并不容易，不僅需要把液態(tài)氦-4轉(zhuǎn)換為固體的冷凍溫度，而且還必須將液態(tài)氦-4加壓到至少25個標準大氣壓。此外氦晶體生長超過1毫米時，還會受到重力的作用而變形。而日本物理學家獨辟蹊徑，在飛機上零重力的條件下，生成長達10毫米的氦晶體，不能不說是一大突破。前些年，像幽靈一樣互相穿過對方的晶體——“超固態(tài)氦”的發(fā)現(xiàn)，引起巨大反響，而這次零重力下生長氦晶體的成功，無疑又是一記重磅炸彈。

Japanese physicists grow helium crystals in zero gravity

Helium crystals are grown under zero gravity conditions by a team of Japanese physicists with the help of a phenomenon called parabolic flight.

A team of Japanese physicists have grown helium crystals in zero gravity conditions. The experiments took place in a small jet under parabolic flight conditions. During parabolic flight, zero gravity was achieved for a duration of 20 seconds. During the two-hour flight, approximately eight experiments were conducted.

Using low temperatures and high pressures, the crystals were grown and splashed with a superfluid. Superfluids are a form of quantum matter which contain zero viscosity and maintain the behavior of a fluid, flowing frictionfree through miniscule gaps.

"Helium crystals can grow from a superfluid extremely fast because the helium atoms are carried by a swift superflow, so it cannot hinder the crystallization process. It has been an ideal material to study the fundamental issues of crystal shape because the crystals form so quickly,” says lead author Professor Ryuji Nomura from The Tokyo Institute of Technology. Nomura states that helium crystals grow from superfluids rapidly because the atoms are carried by a “swift superflow” that does not interfere with crystallization. He adds that because the crystals form so fast, superfluids are an “ideal material” to study crystal shape.

"It can take thousands of years for ordinary classic crystals to reach their final shape; however, at very low temperatures helium crystals can reach their final shape within a second. When helium crystals grow larger than 1 mm they can be easily deformed by gravity, which is why we did our experiments on a plane,” says Nomura.

A small refrigerator fitted with observation windows was taken on the plane. A high-pressure chamber was used to hold large crystals which were then crushed into small pieces with an acoustic wave. A helium-4 superfluid was then applied to the crystal pieces. After being crushed, the tiny crystals were melted, causing larger crystals to grow quickly, with one surviving 10 mm crystal. The other crystals melted in seconds.

The process under which the crystal was grown is called Ostwald ripening. This phenomenon can be seen on ice cream when it’s been in the freezer too long. Large ice crystals form over time, a process commonly known as “freezer burn.”

"Ostwald ripening is usually a very slow process and has never been seen in such huge crystals in a very short period," says Nomura.

The results of the experiments were presented December 13 in the German Physical Society’s New Journal of Physics and the Institute of Physics.

Researchers believe the results of the helium crystal experiments may uncover the fundamentals behind crystal development without the hindrance of gravity.

科學家首次從GRACE信號中成功分離出北美北歐近十年的水量變化趨勢

2002年歐美發(fā)射的重力恢復和氣候?qū)嶒灒℅RACE）衛(wèi)星在探測陸地水儲量變化、冰雪消融取得極大的成功，但是探測北美、北歐和南極地區(qū)的現(xiàn)今質(zhì)量變化趨勢卻遭遇嚴重的挑戰(zhàn)。在末次冰期這些地區(qū)發(fā)育了巨厚的冰蓋，2萬年以來由于古冰蓋的消融，導致現(xiàn)今地殼回彈、地幔物質(zhì)回流。這種冰川均衡調(diào)整引起的質(zhì)量增加在衛(wèi)星重力觀測中產(chǎn)生很強的干擾，甚至完全掩蓋了所探測的現(xiàn)今物質(zhì)平衡信號，雖然GRACE發(fā)射超過十年，但在這些地區(qū)的相關(guān)研究一直沒有取得進展。

中科院測量與地球物理研究所汪漢勝研究員及其負荷研究團隊，在國家杰出青年科學基金、國家基金創(chuàng)新研究群體科學基金等資助下，與加拿大卡爾加里大學胡百卓教授、瑞典國土測量局Holger Steffen博士合作，對冰川均衡調(diào)整理論進行深入研究，首次提出了GRACE聯(lián)合GPS觀測網(wǎng)絡分離現(xiàn)今物質(zhì)平衡信號的有效途徑，在北美中部的加拿大大草原（艾伯塔、薩斯喀徹溫和馬尼托巴省）、五大湖地區(qū)，發(fā)現(xiàn)過去十年陸地水量劇增，每年增加(43.0±5.0)x噸，在北歐斯堪的納維亞半島南部也發(fā)現(xiàn)陸地水量增加，每年增加(2.3±0.8)x 噸。最大的水量增加出現(xiàn)在薩斯喀徹溫省，每年達20mm，揭示了加拿大草原1999年～2005年發(fā)生極端干旱后的水量恢復過程。GRACE 所揭示的水儲量變化均為驗潮站和井中水位觀測所證實，而且傾向于支持歐洲的WGHM水文模型。更為重要的是，這里發(fā)現(xiàn)顯著陸地水量上升，意味著冰融水和降水流進海洋的量減少，因此，如果用海平面上升評估全球變化，則會低估全球變暖的響應。

該研究成果于2012年12月2日發(fā)表在《自然-地球科學》上，論文題目為《GRACE衛(wèi)星重力數(shù)據(jù)揭示北美和斯堪的納維亞半島南部水儲量增加》，該成果被選為“研究亮點”，同時入選與該期刊同期Nature Climate Change的共同網(wǎng)絡焦點（水資源利用）。該研究所提出的途徑能夠從GRACE衛(wèi)星重力信號中排除冰川均衡調(diào)整的巨大干擾，從而有效分離出相關(guān)研究地區(qū)水儲量變化及其趨勢，所給出的結(jié)果有利于了解北美北歐當前知之甚少的區(qū)域水儲量變化趨勢，進一步顯示了衛(wèi)星重力探測地球系統(tǒng)質(zhì)量變化與遷移的巨大能力。該研究對了解地球系統(tǒng)質(zhì)量變化和遷移，特別是對于全球水循環(huán)及其與大氣圈、水圈和海洋的交換過程，具有重要創(chuàng)新性貢獻，也對水資源利用和海平面上升等研究具有重要意義。

Scientists found water storage Increased in North America and Scandinavia from GRACE gravity data

Natural and anthropogenic stresses such as climate change, drought and deluge, increasing water use, land use and agricultural practices affect surface and groundwater resources globally. A small change in the hydrological cycle may have a significant socio-economic impact, which, for example, has recently been observed in the form of groundwater depletion in northwest India probably leading to reduction of agricultural output and shortages of potable water. It is thus of importance to determine the spatial and temporal variability in continental water storage.

The Gravity Recovery and Climate Experiment (GRACE) satellite mission has proved to be an invaluable tool in monitoring such hydrological changes with global coverage and sufficient spatial and temporal resolution. Gravity data from GRACE have revealed trends in present-day continental water storage in many parts of the world. In North America and northern Europe, it has been difficult to provide reliable estimates because of the strong background signals of glacial isostatic adjustment. Attempts to separate the hydrologic signal from the background with numerical models are affected by uncertainties in our understanding of the precise glacial history and mantle viscosity.

Wang Hansheng, a leading scientist in the research project, used a combination of GRACE data and measurements from the global positioning system to separate the hydrological signals without any model assumptions. According to their estimates, water storage in central North America increased by 43.0±5.0 Gt yr-1 over the past decade (Fig1). They attribute this increase to a recovery in terrestrial water storage after the extreme Canadian Prairies drought between 1999 and 2005. They find a smaller rise in water storage in southern Scandinavia, by 2.3±0.8 Gt yr-1. In both North America and Scandinavia, their computed increases in water storage are consistent with longterm observations of terrestrial water level. They suggest that the detected mass gains in terrestrial water storage need to be taken into account in studies on global sea-level rise.Figure1. Hydrology trend rates in North America in equivalent water thickness. a, Using CSR GRACE data and GPS data from ref. 29 in the separation approach. b, Using CSR GRACE data but with ICE-5G(VM2) (ref. 16) model predictions for correction. c,WGHM (ref. 13). d, GLDAS/NOAH (ref. 12) hydrology model. The label A marks the trend peak in the Canadian Prairies and B marks that in the Great Lakes for investigation in Fig. 3. Crosses denote GPS sites. A white line surrounds the investigation area, which depends on a dense GPS network. The area west of the dashed blue line is used for mass change calculation. See Supplementary Fig. S12 for uncertainties.