Experimental observation of spontaneous chaotic current oscillations in GaAs/Al0.45Ga0.55As superlattices at room temperature

Spontaneous self-sustained chaotic current oscillations are observed experimentally in lightly-doped weakly-coupled GaAs/Al0.45Ga0.55As superlattices at room temperature for the first time.The mole fraction of Aluminum in the barrier is chosen to be 0.45 to suppress the thermal carrier leakage through the X-band valley,The effective nonlinearity induced by the sequential well-to-well resonant tunneling can still be strong enough to induce spontaneous chaotic current oscillations even at room temperature,The frequency spectrum of the chaotic current oscillations is ranged from DC to 4 GHz,which can be used as ultra-wide-band noise sources with a bandwidth of several Giga Hertz.     

连铸热坯表面温度可见光谱CCD辐射测温方法

针对连铸坯表面测温现状和存在的问题,建立了双色法(R、G)与单色法(B)相结合的实时测温模型。采用可见光面阵CCD图像传感器进行铸坯表面图像采集,实验研究了不同光圈(F)与积分时间下的R(红)、G(绿)、B(蓝)三基色值随温度的变化规律和动态响应区间。利用计算机图像处理技术建立了连铸热坯表面二维温度场与RGB的关联关系,实现了连铸热坯表面温度场的在线测量。通过控制CCD传感器光积分时间以提高CCD传感器的动态响应范围,为实现连铸坯表面温度场在线测量提供了理论基础和技术支撑。     

液氦超流转变温度复现性研究

利用液氦超流转变时超流氦（He Ⅱ）与正常氦（He Ⅰ）热导率突变的性质复现液氦超流转变温度T_λ。采用带毛细管结构的小型密封瓶,通过控温将微小热流通过小型密封瓶毛细管,实现毛细管中He Ⅰ/He Ⅱ两相共存,并使He Ⅰ/He Ⅱ界面停留在毛细管中,从而获得稳定、平坦的液氦超流转变温坪。利用毛细管热流对液氦超流转变温度的下压效应,得到不同热流的多个温坪,进一步利用外推法求得零热流下真实的T_λ值。24次液氦超流转变温度复现实验结果表明,标准偏差为0.022mK,证明了液氦超流转变温度具有良好的稳定性和复现性,推荐将液氦超流转变温度作为国际温标的固定点使用。     

Probable observation of a supersolid helium phase

When liquid (4)He is cooled below 2.176 K, it undergoes a phase transition-Bose-Einstein condensation-and becomes a superfluid with zero viscosity. Once in such a state, it can flow without dissipation even through pores of atomic dimensions. Although it is intuitive to associate superflow only with the liquid phase, it has been proposed theoretically that superflow can also occur in the solid phase of (4)He. Owing to quantum mechanical fluctuations, delocalized vacancies and defects are expected to be present in crystalline solid (4)He, even in the limit of zero temperature. These zero-point vacancies can in principle allow the appearance of superfluidity in the solid. However, in spite of many attempts, such a 'supersolid' phase has yet to be observed in bulk solid (4)He. Here we report torsional oscillator measurements on solid helium confined in a porous medium, a configuration that is likely to be more heavily populated with vacancies than bulk helium. We find an abrupt drop in the rotational inertia of the confined solid below a certain critical temperature. The most likely interpretation of the inertia drop is entry into the supersolid phase. If confirmed, our results show that all three states of matter-gas, liquid and solid-can undergo Bose-Einstein condensation.     

Non-equilibrium degassing and a primordial source for helium in ocean-island volcanism

Radioactive decay of uranium and thorium produces 4He, whereas 3He in the Earth's mantle is not produced by radioactive decay and was only incorporated during accretion-that is, it is primordial. 3He/4He ratios in many ocean-island basalts (OIBs) that erupt at hotspot volcanoes, such as Hawaii and Iceland, can be up to sixfold higher than in mid-ocean ridge basalts (MORBs). This is inferred to be the result of outgassing by melt production at mid-ocean ridges in conjunction with radiogenic ingrowth of 4He, which has led to a volatile-depleted upper mantle (MORB source) with low 3He concentrations and low 3He/4He ratios. Consequently, high 3He/4He ratios in OIBs are conventionally viewed as evidence for an undegassed, primitive mantle source, which is sampled by hot, buoyantly upwelling deep-mantle plumes. However, this conventional model provides no viable explanation of why helium concentrations and elemental ratios of He/Ne and He/Ar in OIBs are an order of magnitude lower than in MORBs. This has been described as the 'helium concentration paradox' and has contributed to a long-standing controversy about the structure and dynamics of the Earth's mantle. Here we show that the helium concentration paradox, as well as the full range of noble-gas concentrations observed in MORB and OIB glasses, can self-consistently be explained by disequilibrium open-system degassing of the erupting magma. We show that a higher CO2 content in OIBs than in MORBs leads to more extensive degassing of helium in OIB magmas and that noble gases in OIB lavas can be derived from a largely undegassed primitive mantle source.     

Observation of the ideal Josephson effect in superfluid 4He

Superfluids and superconductors are the only states of condensed matter that can be described by a single wavefunction, with a coherent quantum phase Phi. The mass flow in a superfluid can be described by classical hydrodynamics for small flow velocity, but above a critical velocity, quantized vortices are created and the classical picture breaks down. This can be observed for a superfluid flowing through a microscopic aperture when the mass flow is measured as a function of the phase difference across the aperture; the curve resembles a hysteretic sawtooth where each jump corresponds to the creation of a vortex. When the aperture is made small enough, the system can enter the so-called 'ideal' Josephson regime, where the superfluid mass flow becomes a continuous function of the phase difference. This regime has been detected in superfluid 3He, but was hitherto believed to be unobservable, owing to fluctuations, in 4He. Here we report the observation of the ideal Josephson effect in 4He. We study the flow of 4He through an array of micro-apertures and observe a transition to the ideal Josephson regime as the temperature is increased towards the superfluid transition temperature, Tlambda.     

Noble gas isotopic compositions of deep carbonate rocks from the Tarim Basin

Abundances and isotopic compositions of noble gases (He, Ne, Ar, Kr) with various existence states in carbonate rocks from the Tacan1 Well have been investigated by means of the stepwise heating technique. The elemental abundance patterns of noble gases in the samples show the enrichment of heavy noble gases and depletion of ²⁰Ne relative to the atmosphere, which are designated as type-Ⅰand are similar to that observed in water, natural gases and sedimentary rocks. The ³He/⁴He ratios of deep carbonate samples at lower and medium temperature (300—700℃) and a majority of samples at higher temperature (1100—1500℃) steps are very similar to those of natural gases in the same strata in this area, this feature of radiogenic crustal helium shows that the Tazhong Uplift is relatively stable. However, significant helium and argon isotopic anomalies are found at the 1100℃ step in the Middle-Upper Ordovician carbonate rock, suggesting the incorporation of mantle-derived volatiles, this may be due to minor igneous minerals contained in sedimentary carbonate rocks. The ⁴⁰Ar/ ³⁶Ar ratios in the Cambrian carbonate rock are slightly higher than those in Ordovician carbonate rocks, which may reflect the influence of the chronologic accumulation effect of crust radiogenic ⁴⁰Ar. Argon isotopes of various existence states in source rocks are much more different, both ³⁸Ar/ ³⁶Ar and ⁴⁰Ar/ ³⁶Ar ratios at the higher temperature steps are higher than those at the lower temperature steps.     

Periodic oscillations in millennial global-mean temperature and their causes

Time series of solar radiation and north Pacific sea surface temperature (SST) index were used to analyze their causality relationship with various periodic oscillations in reconstructed millennial global-mean temperature series. The three long-term periods of the Medieval Warm Period (MWP), Little Ice Age (LIA) and recent Global Warming Period (GWP) were distinct in the temperature series. 21-year, 65-year, 115-year and 200-year oscillations were derived from the temperature series after removing three long-term climatic temperatures. The phases of temperature oscillations significantly lagged behind oceanic SST and solar radiation variability. The recent decadal warm period was caused by the quasi-21-year temperature oscillation. At this century-cross period, the four oscillations reached their peaks simultaneously, which did not occur during the last millennium. Based on the long-term trend during the GWP and the four periodic oscillations, global-mean temperature is expected to drop to a new cool period in the 2030s and then a rising trend would be towards to a new warm period in the 2060s.     

Evolution of helium isotopes in the Earth's mantle

Degassing of the Earth's mantle through magmatism results in the irreversible loss of helium to space, and high (3)He/(4)He ratios observed in oceanic basalts have been considered the main evidence for a 'primordial' undegassed deep mantle reservoir. Here we present a new global data compilation of ocean island basalts, representing upwelling 'plumes' from the deep mantle, and show that island groups with the highest primordial signal (high (3)He/(4)He ratios) have striking chemical and isotopic similarities to mid-ocean-ridge basalts. We interpret this as indicating a common history of mantle trace element depletion through magmatism. The high (3)He/(4)He in plumes may thus reflect incomplete degassing of the deep Earth during continent and ocean crust formation. We infer that differences between plumes and the upper-mantle source of ocean-ridge basalts reflect isolation of plume sources from the convecting mantle for approximately 1-2 Gyr. An undegassed, primordial reservoir in the mantle would therefore not be required, thus reconciling a long-standing contradiction in mantle dynamics.     

四氮杂大环镍(Ⅱ)配合物催化的化学振荡反应

:报道了一种反式Curtis环镍 (Ⅱ )的配合物NiL(ClO4) 2 (L为 5,5,7,1 2 ,1 2 ,1 4-六甲基 - 1 ,4,8,1 1 -四氮杂十四环 - 7,1 4-二烯 )催化NaBrO3—CH2 (COOH) 2 (MA)—H3PO4体系的化学振荡反应。测得该体系的振荡范围 ,研究了各物种浓度、自由基抑制剂和还原剂、Ag+,Hg2 +以及温度对振荡反应的影响。记录了反应的振荡轨迹。     

榛子花粉形态变异与环境关系

应用典范相关分析法对榛子花粉形态指标与气候因子相关关系进行了研究。结果表明，榛子花粉形态指标中，萌发孔数与年相对湿度呈极紧密负相关，与年降水量呈紧密正相关，与年平均温度呈负相关；极轴长／赤轴长、最短的萌发孔间距离／所对的赤轴长与年日照时间呈紧密正相关，与年平均温度呈负相关；萌发孔直径与年相对湿度呈弱的正相关。     

曝气器的最优孔径分析

根据曝气过程中氧转移的有关理论，推导出需气量的表达式；并通过曝气过程中能量消耗的分析．导出动力消耗的表达式．通过计算分析得出，在一定的条件下，曝气器有最优孔径．一般水深在4m左右．曝气器的最优孔径最小．一定孔径的曝气器．存在最佳安装水深，最佳安装水深随曝气器孔径的增大而增长．水深较小时．宜选用孔径较小的曝气器；水深较大时，宜选用孔径较大的曝气器．一般情况下．采用浅水曝气是不利的．     

Effects of helium on titanium films and the helium diffusion

Using direct current-magnetron sputtering, Helium-trapped Ti films with a He/Ar mixture was studied. The relative helium content, helium depth profiles for the Ti films and crystallization capacity were analyzed by Enhanced Proton Backscattering Spectrometry （EPBS） and X-ray diffraction （XRD）. It was found that helium diffusion enhanced as more helium trapping into Ti films, and the He holding ratios were 95.9%, 94.9%, 93.9%, 82.8% when the Ti films with the He/Ti of concentrations of 9.7 at.%, 19.5 at.%, 19.7 at.%, 48.3 at.% were measured again 4 months later, respectively. The diffraction peaks became weak and wider, the peak of （002） plane was shifted to smaller diffraction angles and the relevant interplanar spacing d（hk,） increased gradually as more helium trapping into Ti films. The main peak was made trending to the （101） plane by both higher deposition temperature and more helium trapping.     

准一维电子通道中声电电流的实验研究

在甚低温（0．236K）下，通过实验研究了叉指换能器的频率特性以及准一维电子通道中不同源漏电流与分裂门负电位的关系，获得了分裂门的钳断电压．经观察表面声波搬运电子通过准一维电子通道的声电电流发现，声电电流可随分裂门负偏压的变化而发生振荡，作者用库仑阻塞理论对这一现象作了解释．     

Probable heat capacity signature of the supersolid transition

Liquid 4He enters the superfluid state and flows without friction below 2.176 K. Thin liquid films adsorbed on solid substrates undergo the same transformation, although at a lower temperature. When the substrate is subjected to oscillatory motion a portion of the film, known as the superfluid fraction, decouples from the oscillation. A similar phenomenon has been observed in solid 4He, in which a fraction of the solid seems to decouple from the motion of the surrounding lattice. Although this observation has been replicated in various laboratories, no thermodynamic signature of the possible supersolid transition has been seen. Here we report the finding of a heat capacity peak that coincides with the onset of mass decoupling. This complementary experimental evidence supports the existence of a genuine transition between the normal solid and supersolid phases of 4He.     

Mantle thermal pulses below the Mid-Atlantic Ridge and temporal variations in the formation of oceanic lithosphere

A 20-Myr record of creation of oceanic lithosphere is exposed along a segment of the central Mid-Atlantic Ridge on an uplifted sliver of lithosphere. The degree of melting of the mantle that is upwelling below the ridge, estimated from the chemistry of the exposed mantle rocks, as well as crustal thickness inferred from gravity measurements, show oscillations of approximately 3-4 Myr superimposed on a longer-term steady increase with time. The time lag between oscillations of mantle melting and crustal thickness indicates that the mantle is upwelling at an average rate of approximately 25 mm x yr(-1), but this appears to vary through time. Slow-spreading lithosphere seems to form through dynamic pulses of mantle upwelling and melting, leading not only to along-axis segmentation but also to across-axis structural variability. Also, the central Mid-Atlantic Ridge appears to have become steadily hotter over the past 20 Myr, possibly owing to north-south mantle flow.     

Observation of the antimatter helium-4 nucleus

High-energy nuclear collisions create an energy density similar to that of the Universe microseconds after the Big Bang; in both cases, matter and antimatter are formed with comparable abundance. However, the relatively short-lived expansion in nuclear collisions allows antimatter to decouple quickly from matter, and avoid annihilation. Thus, a high-energy accelerator of heavy nuclei provides an efficient means of producing and studying antimatter. The antimatter helium-4 nucleus (4He), also known as the anti-α (α), consists of two antiprotons and two antineutrons (baryon number B = -4). It has not been observed previously, although the α-particle was identified a century ago by Rutherford and is present in cosmic radiation at the ten per cent level. Antimatter nuclei with B?相似文献   

交流电润湿作用下液滴的振荡行为特性

摘要：
实验研究了不同交流电频率下共面电极电润湿芯片上液滴的振荡行为特性.结果表明,在某些特定的输入频率下液滴出现共振,共振模态称为Pn（n=2,4,…）,且实验获得的共振频率值与线性理论预测值吻合良好.在共振模态Pn下,液滴振荡对称,表面呈现n/2个波峰.在相邻共振模态间存在某个临界频率,此时液滴振荡对称,但很微弱,且接触线宽度和液滴高度的振荡相位关系发生转变.小于此临界频率时,液滴接触线延展至最大时呈液瓣状,且液瓣的位置通过液滴的收缩和延展在水平面内周期性交替,液瓣数目随着相邻共振模态阶数n的升高而增加.大于此临界频率时,液滴振荡左右不对称,具体表现为液滴表面波的传动.预期这些液滴的非对称振荡会产生更为混乱的内部流动,从而增强微流控液滴混合器的混合效率.
     

An intense stratospheric jet on Jupiter

The Earth's equatorial stratosphere shows oscillations in which the east-west winds reverse direction and the temperatures change cyclically with a period of about two years. This phenomenon, called the quasi-biennial oscillation, also affects the dynamics of the mid- and high-latitude stratosphere and weather in the lower atmosphere. Ground-based observations have suggested that similar temperature oscillations (with a 4-5-yr cycle) occur on Jupiter, but these data suffer from poor vertical resolution and Jupiter's stratospheric wind velocities have not yet been determined. Here we report maps of temperatures and winds with high spatial resolution, obtained from spacecraft measurements of infrared spectra of Jupiter's stratosphere. We find an intense, high-altitude equatorial jet with a speed of approximately 140 m s(-1), whose spatial structure resembles that of a quasi-quadrennial oscillation. Wave activity in the stratosphere also appears analogous to that occurring on Earth. A strong interaction between Jupiter and its plasma environment produces hot spots in its upper atmosphere and stratosphere near its poles, and the temperature maps define the penetration of the hot spots into the stratosphere.     

Brain-state- and cell-type-specific firing of hippocampal interneurons in vivo

Neural-network oscillations at distinct frequencies have been implicated in the encoding, consolidation and retrieval of information in the hippocampus. Some GABA (gamma-aminobutyric acid)-containing interneurons fire phase-locked to theta oscillations (4-8 Hz) or to sharp-wave-associated ripple oscillations (120-200 Hz), which represent different behavioural states. Interneurons also entrain pyramidal cells in vitro. The large diversity of interneurons poses the question of whether they have specific roles in shaping distinct network activities in vivo. Here we report that three distinct interneuron types--basket, axo-axonic and oriens-lacunosum-moleculare cells--visualized and defined by synaptic connectivity as well as by neurochemical markers, contribute differentially to theta and ripple oscillations in anaesthetized rats. The firing patterns of individual cells of the same class are remarkably stereotyped and provide unique signatures for each class. We conclude that the diversity of interneurons, innervating distinct domains of pyramidal cells, emerged to coordinate the activity of pyramidal cells in a temporally distinct and brain-state-dependent manner.