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81.
Treussart F Alléaume R Le Floc'h V Xiao LT Courty JM Roch JF 《Physical review letters》2002,89(9):093601
We studied intensity fluctuations of a single photon source relying on the pulsed excitation of the fluorescence of a single molecule at room temperature. We directly measured the Mandel parameter Q(T) over 4 orders of magnitude of observation time scale T by recording every photocount. On time scale of a few excitation periods, sub-Poissonian statistics is clearly observed and the probablility of two-photons events is 10 times smaller than Poissonian pulses. On longer times, blinking in the fluorescence, due to the molecular triplet state, produces an excess of noise. 相似文献
82.
We present a study on the fluctuations of semiflexible actin filaments using fluorescence videomicroscopy, focusing on the end-to-end fluctuations of single filaments. In order to specifically measure the position of the polymer's ends, we developed a novel noninvasive method that consists of annealing short end tags to the filaments. This allows us to probe polymer fluctuations to a very high accuracy. We compared the distribution of the end-to-end distance with recent theoretical results, and found excellent agreement. We also studied the dynamics of the mean-square end-to-end distance deltaR2(t) and orientation of the ends, deltaTheta(2)(t), finding power laws t(3/4) and t(1/4), respectively. Scaling behavior for deltaR2(t) is observed over several decades in relaxation time in agreement with theoretical results. 相似文献
83.
Badro J Fiquet G Struzhkin VV Somayazulu M Mao HK Shen G Le Bihan T 《Physical review letters》2002,89(20):205504
We present a new method to separate the crystallographic and electronic phase transitions in hematite using x-ray emission spectroscopy and x-ray diffraction. Our observations, based on the behavior of a metastable high-pressure phase in the stability domain of the low-pressure phase, show that the electronic transition is preempted by the crystallographic transition. The former occurs only afterwards in the high-pressure phase, possibly as a result of a Mott transition. The idea that the electronic transition drives the transition in hematite is therefore invalidated. Such methods should help elucidate the mechanics and the driving forces behind a number of first-order high-pressure phase transitions. 相似文献
84.
The α preformation factor and penetration probability
have been analyzed for even--even nuclei of Po, Rn, Ra using
experimental released energies and α decay half-lives in the
frame of the double folding model. It is shown that N=126 is a neutron
magic number from α preformation and shell effects play
an important role in α preformation. The closer the
nucleon number is to the magic number, the more difficult α
formation in the parent nucleus is. The preformation factor can
supply information on the nuclear structure and the penetration
probability mainly determines α decay half-life. 相似文献
85.
Magnetic resonance imaging (MRI) is commonly used as part of the assessment of patients presenting with leg/back pain to the orthopedic spinal outpatient clinic. Abdominal aortic aneurysm (AAA) can cause symptoms often similar to those of spinal stenosis. We report a case series of four patients who had incidental AAA detected on lumbosacral MRI. All patients were suffering from degenerative spinal disease and had been referred to the orthopedic spinal clinic. After history, examination and review of the imaging, all patients were referred to a vascular surgeon, and three were found to be completely asymptomatic from their aneurysm. One patient required open repair with an aortic graft due to the size of the aneurysm, although his symptoms were attributable to his spinal disease. All patients still required management of their degenerative spinal disease after their vascular review. We can find no other case reports of AAA as an incidental finding on lumbosacral MRI. This case series highlights the importance of looking at all aspects of our imaging and remembering the nonspinal causes of back and leg pains. Furthermore, in the presence of AAA when managing patients in the orthopedic outpatient setting, the authors recommend vascular review before offering orthopedic interventional management options to these patients. 相似文献
86.
Abstract A synchrotron X-ray diffraction study on hexagonal graphite-like boron nitride (h-BN) was performed under high pressures and temperatures. From the measured P-V-Trelation for h-BN (with a three-dimensional ordering parameter P3 = 0.9) in the temperature range from 298 to 1273 K and up to 6.7 GPa, the thermoelastic parameters are derived by fitting a modified high temperature Birch-Murnaghan equation of state. The results are: bulk modulus B0[GPa] = 27.6-0.0081(T[K]-298) and its pressure derivative B1 = 10.5 + 0.0016(T [K] - 298). These values are for samples with P3 = 0.9 and are quite different for samples with different values of the order parameter. This parameter is shown to have a leading role in the determination of the thermoelastic properties of h-BN, which explains and reconciles the differences between previous results. 相似文献
87.
We have analyzed the constant loss contribution to the ac conductivity in the frequency range 10 Hz-1 MHz and temperatures down to 8 K, for two Li ionic conductors, one crystalline (Li(0.18)La(0.61)TiO(3)) and the other glassy (61SiO(2);35Li(2)O.3Al(2)O3.P(2)O(5)). As temperature is increased a crossover is observed from a nearly constant loss to a fractional power law frequency dependence of the ac conductivity. At any fixed frequency omega, this crossover occurs at a temperature T such that omega approximately nu(0)exp(-E(m)/k(B)T), where nu(0) is the attempt frequency and E(m) is identified with the barrier for Li+ ions to leave their wells. 相似文献
88.
Critical-point phase separation in laser ablation of conductors 总被引:1,自引:0,他引:1
Vidal F Johnston TW Laville S Barthélemy O Chaker M Le Drogoff B Margot J Sabsabi M 《Physical review letters》2001,86(12):2573-2576
Laser ablation due to an ultrashort laser pulse on a massive aluminum target was investigated by means of a one-dimensional fluid code. Clear separation between the ablated matter and the unablated target is seen to occur through spinodal decomposition involving thermodynamic instabilities near the critical point of aluminum. The code also shows that the end of the ablation process is preceded by the ejection of droplets, which form about 15% of the total ejected mass. 相似文献
89.
Applying Kontsevich's iterated integral for tangles, we get an isotopy invariant of tangles. We give a method to compute the integral of a tangle combinatorially from modified integrals of some simple tangles. We localize the integral by moving the end points of the tangle to an extreme configuration, and modify the integral so that it is convergent. By using a similar technique, we generalize Kontsevich's invariant to a framed tangle. 相似文献
90.
A scheme to perfectly preserve an initial qubit state in
geometric quantum computation is proposed for a single-qubit geometric
quantum gate in a nuclear magnetic resonance system. At first, by
adjusting some magnetic field parameters, one can let the dynamic
phase be proportional to the geometric phase. Then, by controlling
the azimuthal angle in the initial state, we may realize a
geometric quantum gate whose fidelity is equal to one under
cyclic evolution. This means that the quantum information is no
distortion in the process of geometric quantum computation. 相似文献