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排序方式: 共有1173条查询结果,搜索用时 828 毫秒
31.
We report preliminary results of the first heat capacity measurements on atomically layered
3
He –
4
He mixture films adsorbed on the surface of graphite. The
4
He film consists of two solid and two superfluid atomic layers. The heat capacity has been investigated over the range 1 – 70mK as a function of the surface density of
3
He atoms added to the film. At coveragesn3
< 4nm
–2
, the
3He forms a uniform two dimensional Fermi system. The coverage dependence of the linear coefficient of the heat capacity, , allows a determination of the hydrodynamic effective mass and
. At higher coverages a step-like increase in is observed, interpreted as the formation of a second two dimensional Fermi system. 相似文献
32.
R.M. Bowley A.D. Armour J. Nyéki B.P. Cowan J. Saunders 《Journal of Low Temperature Physics》1998,113(3-4):399-404
We analyse recent observations, using a torsional oscillator, of the superfluid transition of a fluid
4
He bilayer, within the framework of a modified dynamic theory of the Kosterlitz-Thouless transition. A parametric plot of the real and imaginary parts of the complex superfluid density, determined from the measured period shift and dissipation, achieves a high degree of collapse of the experimental data at different coverages onto a universal curve. This is compared with the result of the recent theory. 相似文献
33.
We present the fabrication and characterization of nanoscale fluidic channels with embedded electrodes. Arrays of 2.25 μm
long and 60 nm tall nanochannels with widths ranging from 60 to 500 nm were microfabricated in SiO2 with Au electrodes embedded inside and outside of the nanochannels. The built-in electrodes were able to probe nanochannel
conductance via a redox reaction of
\textFe(\textCN)63 - /4 - {\text{Fe}}({\text{CN}})_{6}^{3 - /4 - } . Amperometric characterization showed that conductance of nanochannel arrays varied linearly both with the width and number
of nanochannels and was in the 10–100 pS range. Further, we show that electrical current was largely diffusion based and could
be predicted from channel geometry using standard diffusion equations. We also discuss the potential of such nanochannel arrays
as electronic biomolecular sensors and show preliminary streptavidin detection results. 相似文献
34.
Kikuhito Kawasue Shoji Sakai Terufumi Wakiyama Shigeki Oyama Hisashi Senda 《Artificial Life and Robotics》2008,13(1):336-340
The 3D quantitative measurement system for a sewer pipe is introduced. Two parallel lasers are rotated by the motor and draw
the two annular streaks on the inside surface of the pipe. The circular laser streaks are recorded by the CCD camera. The
measurement of the cross-section is established by analyzing the recorded streaks. The tilt of the robot against the axis
of the pipe is detected by the deviation between two parallel lasers. It enables us to measure the vertical cross section
of the pipe regardless the tilt of the system to the pipe. Experimental result shows the feasibility of the system.
This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January
31–February 2, 2008 相似文献
35.
Vesa Halava Tero Harju Juhani Karhumki Michel Latteux 《Theoretical computer science》2007,380(3):355-362
In the Post Correspondence Problem (PCP) an instance (h,g) consists of two morphisms h and g, and the problem is to determine whether or not there exists a nonempty word w such that h(w)=g(w). Here we prove that the PCP is decidable for instances with unique blocks using the decidability of the marked PCP. Also, we show that it is decidable whether an instance satisfying the uniqueness condition for continuations has an infinite solution. These results establish a new and larger class of decidable instances of the PCP, including the class of marked instances. 相似文献
36.
Possible Phase Transition at Low mK Temperatures in Liquid Helium Mixture Films Adsorbed on Graphite
F. Ziouzia H. Patel J. Nyéki B. P. Cowan J. Saunders 《Journal of Low Temperature Physics》2004,134(1-2):79-84
We report heat capacity and magnetisation measurements of 3He adsorbed on the surface of graphite plated with three atomic layers of 4He. For 3He coverages n 3>4 nm?2 the heat capacity corresponds to a 2D Fermi fluid. The inferred hydrodynamic mass of the 3He quasiparticles is 1.38±0.05 m3. The 3He effective mass ratio increases with coverage to 2.4 at n 3=4 nm?2, due to Fermi liquid interactions. The heat capacity isotherm exhibits a steplike increase centred on n 3=4.5 nm?2, similar to that previously observed on four layers of 4He. This is associated with the population of the first excited Andreev surface bound state. However, in the present case, as n 3 is increased through the step a pronounced anomalous feature develops in the temperature dependence of the heat capacity, around 10 mK. Below 5 mK the heat capacity is approximately linear in temperature. With n 3=7 nm?2, we find that this behaviour is very sensitive to small changes in the 4He third layer coverage, around the completed third layer. Measurements of the 3He magnetisation,, by continuous wave NMR methods, find a significant increase with decreasing temperature below around 20 mK. Together the data suggest that a phase transition takes place in the film at low mK temperatures. 相似文献
37.
38.
Coral Moctezuma Almuth Hammerbacher Martin Heil Jonathan Gershenzon Rodrigo Méndez-Alonzo Ken Oyama 《Journal of chemical ecology》2014,40(5):458-467
The role of plant polyphenols as defenses against insect herbivores is controversial. We combined correlative field studies across three geographic regions (Northern Mexico, Southern Mexico, and Costa Rica) with induction experiments under controlled conditions to search for candidate compounds that might play a defensive role in the foliage of the tropical oak, Quercus oleoides. We quantified leaf damage caused by four herbivore guilds (chewers, skeletonizers, leaf miners, and gall forming insects) and analyzed the content of 18 polyphenols (including hydrolyzable tannins, flavan-3-ols, and flavonol glycosides) in the same set of leaves using high performance liquid chromatography and mass spectrometry. Foliar damage ranged from two to eight percent per region, and nearly 90% of all the damage was caused by chewing herbivores. Damage due to chewing herbivores was positively correlated with acutissimin B, catechin, and catechin dimer, and damage by mining herbivores was positively correlated with mongolinin A. By contrast, gall presence was negatively correlated with vescalagin and acutissimin B. By using redundancy analysis, we searched for the combinations of polyphenols that were associated to natural herbivory: the combination of mongolinin A and acutissimin B had the highest association to herbivory. In a common garden experiment with oak saplings, artificial damage increased the content of acutissimin B, mongolinin A, and vescalagin, whereas the content of catechin decreased. Specific polyphenols, either individually or in combination, rather than total polyphenols, were associated with standing leaf damage in this tropical oak. Future studies aimed at understanding the ecological role of polyphenols can use similar correlative studies to identify candidate compounds that could be used individually and in biologically meaningful combinations in tests with herbivores and pathogens. 相似文献
39.