共查询到20条相似文献,搜索用时 31 毫秒
1.
Dipak Ghosh Argha Deb Asok Kumar Mallick Sharmil Asarkar Krishnadas Purkait Ranjan Sengupta 《Pramana》2004,63(5):963-968
In this paper intermittent behaviour of the pions from ‘cold’ and ‘hot’ classes of events from12C-AgBr interactions at 4.5 A GeV has been studied, separately. The results reveal strong intermittent pattern in case of ‘cold’
class of events. 相似文献
2.
Recent observations of a direct reaction between adsorbates and hydrogen atoms incident from the gas phase are interpreted in terms of an Eley-Rideal reaction. A detailed comparison of the experimental data for the HD/Cu(111) system with quantum mechanical model calculations corroborates such an interpretation. The peculiar isotope effect observed can be understood from the different dynamical implications of appropriately rescaled potential energy surfaces. The width of the measured time-of-flight spectrum is explained from the overlapping contributions of the populated vibrational levels. The angular distributions are rationalized by contributions both from 'indirect' events, where the incident atoms make several bounces in the surface well prior to reaction, and 'direct' reactive events. 相似文献
3.
Recent observations of a direct reaction between adsorbates and hydrogen atoms incident from the gas phase are interpreted in terms of an Eley-Rideal reaction. A detailed comparison of the experimental data for the HD/Cu(111) system with quantum mechanical model calculations corroborates such an interpretation. The peculiar isotope effect observed can be understood from the different dynamical implications of appropriately rescaled potential energy surfaces. The width of the measured time-of-flight spectrum is explained from the overlapping contributions of the populated vibrational levels. The angular distributions are rationalized by contributions both from ‘indirect’ events, where the incident atoms make several bounces in the surface well prior to reaction, and ‘direct’ reactive events. 相似文献
4.
C.-W. Chen C.-H. Lin H.-P. Chiang Y.-C. Liu P.T. Leung W.S. Tse 《Applied Physics A: Materials Science & Processing》2007,89(2):377-380
The temperature dependence of the sensitivity of an optical sensor based on long-range surface plasmon resonance (LRSPR) is
studied via theoretical modeling. Both the ‘angular interrogation’ and the ‘wavelength interrogation’ modes of operation are
studied. In addition, the variation of the full width at half maximum of the LRSPR ‘reflectance dip’ is also studied as a
function of temperature, which ultimately determines the temperature dependence of the sensitivity of the sensor when the
reflectance is monitored at a fixed incident angle (‘reflectance interrogation’). It is found that while most of the time
only the ‘reflectance interrogation’ mode leads to improved sensitivity for the LRSPR sensor compared to a conventional SPR
sensor, the temperature stability of the operation of the LRSPR sensor is generally higher than (or at least comparable to)
that of the SPR sensor.
PACS 73.20.Mf; 07.07.Df 相似文献
5.
Thin-film transistors were made using 50-nm-thick directly deposited nanocrystalline silicon channel layers. The transistors
have a coplanar top gate structure. The nanocrystalline silicon was deposited from discharges in silane, hydrogen and silicon
tetrafluoride. The transistors combine a high electron field effect mobility of ∼10 cm2 V-1s-1 with a low ‘off’ current of ∼10-14 A per μm of channel length and an ‘on’/‘off’ current ratio of ∼108. This result shows that transistors made from directly deposited silicon can combine high mobility with low ‘off’ currents.
Received: 28 May 2001 / Accepted: 30 May 2001 / Published online: 30 August 2001 相似文献
6.
J. Reichel W. Hänsel P. Hommelhoff T.W. Hänsch 《Applied physics. B, Lasers and optics》2001,72(1):81-89
Lithographically fabricated circuit patterns can provide magnetic guides and microtraps for cold neutral atoms. By combining
several such structures on the same ceramic substrate, we have realized the first ‘atom chips’ that permit complex manipulations
of ultracold trapped atoms or de Broglie wave packets. We show how to design magnetic potentials from simple conductor patterns
and we describe an efficient trap-loading procedure in detail. Applying the design guide, we describe some new microtrap potentials,
including a trap which reaches the Lamb–Dicke regime for rubidium atoms in all three dimensions, and a rotatable Ioffe–Pritchard
trap, which we also demonstrate experimentally. Finally, we demonstrate a device allowing independent linear positioning of
two atomic clouds which are very tightly confined laterally. This device is well suited for the study of one-dimensional collisions.
Received: 27 July 2000 / Revised version: 30 August 2000 / Published online: 22 November 2000 相似文献
7.
J. Reichel 《Applied physics. B, Lasers and optics》2002,74(6):469-487
The article gives an overview of the rapidly evolving field of magnetic microchip traps (also called ‘atom chips’) for neutral
atoms. Special attention is given to Bose–Einstein condensation in such traps, to the particular properties of microchip trap
potentials, and to practical considerations in their design. Scaling laws are developed, which lead to an estimate of the
ultimate confinement that chip traps can provide. Future applications such as integrated atom interferometers are discussed.
Received: 28 March 2002 / Published online: 14 May 2002 相似文献
8.
E. Bodenstedt 《Hyperfine Interactions》1985,25(1-4):521-537
A survey over the present state of the empirical investigation of the electric field gradient at the nuclear site of impurity
atoms and of matrix atoms in noncubic metal matrices is given. A qualitative explanation in terms of the electronic charge
distribution typical for the host's group in the periodic system of elements is discussed. For group IIb hosts, two semi-empirical
models which were developed in Bonn are described in more detail, i.e. the ‘naive model’ and the ‘Thomas-Fermi model’. 相似文献
9.
This review details a now established area within the isonitrile multi-component reaction (IMCR) field of study, namely employing
bi-functional reagents in the Ugi reaction for the construction of screening sets with the additional element or even possibly
‘metric’ of enhanced ‘iterative efficiency potential’ The concept of ‘iterative efficiency’ will be briefly introduced, coupled
with discussion on new synthetic routes to select bi-functional IMCR precursors and their use in the generation of pharmacologically
relevant ‘molecular diversity’ 相似文献
10.
D. Schrader S. Kuhr W. Alt M. Müller V. Gomer D. Meschede 《Applied physics. B, Lasers and optics》2001,73(8):819-824
Using optical dipole forces we have realized controlled transport of a single or any desired small number of neutral atoms
over a distance of a centimeter with sub-micrometer precision. A standing wave dipole trap is loaded with a prescribed number
of cesium atoms from a magneto-optical trap. Mutual detuning of the counter-propagating laser beams moves the interference
pattern, allowing us to accelerate and stop the atoms at preselected points along the standing wave. The transportation efficiency
is close to 100%. This optical ‘single-atom conveyor belt’ represents a versatile tool for future experiments requiring deterministic
delivery of a prescribed number of atoms on demand.
Received: 6 July 2001 / Published online: 23 November 2001 相似文献
11.
A. Waxman M. Givon G. Aviv D. Groswasser R. Folman 《Applied physics. B, Lasers and optics》2009,95(2):301-305
The influence of Zn-atom additive on ‘pure’ copper vapor laser output characteristics is studied. The laser pulse width, energy
and power are found to increase under the diffusion of zinc atoms from a zinc-containing reservoir into the discharge of the
copper-vapor laser at temperatures above 500°C. Additional absorption experiments and calculations are consistent with the
conclusion that not only optical resonant pumping by the 213.9-nm Zn I line, but also other processes, should be taken into
account to explain the effects of additive influence. 相似文献
12.
We describe the present status of coupled-state calculations for positron scattering by ‘one-electron’ atoms. We show how
pseudostates are used to represent the continuum channels. Illustrative results from positron scattering by atomic hydrogen
and the alkali metals are presented. 相似文献
13.
Controlled plasmon coupling is observed in nanoparticle assemblies composed of 20 nm silver ‘satellite’ nanoparticles tethered
by reconfigurable duplex DNA linkers to a 50 nm gold ‘core’ particle. The assemblies incorporate silver nanoparticle–oligonucleotide
conjugates prepared using a new conjugation method in which the recognition strand is anchored by a 10 base pair, double strand
spacer that presents adjacent 3’- and 5’-thiols to the silver surface. Reconfiguration of the DNA linkers from a compact to
an extended state results in decreased core–satellite coupling and a blue-shift in the gold core plasmon resonance. The structural
basis for the observed resonance modulation is investigated through simulation of the scattering spectra of binary assemblies
with various core–satellite separations. Additional simulations of core–satellite assemblies composed of gold satellite particles
bound to silver cores and of assemblies composed entirely of silver particles are used to clarify the dependence of the coupling
response on the composition of the components and their distribution within the assembly.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
14.
C. Henkel P. Krüger R. Folman J. Schmiedmayer 《Applied physics. B, Lasers and optics》2003,76(2):173-182
The limitations for the coherent manipulation of neutral atoms with fabricated solid-state devices, so-called ‘atom chips’,
are addressed. Specifically, we examine the dominant decoherence mechanism, which is due to the magnetic noise originating
from the surface of the atom chip. It is shown that the contribution of fluctuations in the chip wires at the shot-noise level
is not negligible. We estimate the coherence times and discuss ways to increase them. Our main conclusion is that future advances
should allow for coherence times as long as 1 s, a few μm away from the surface.
Received: 22 August 2002 / Revised version: 30 October 2002 / Published online: 26 February 2003
RID="*"
ID="*"Corresponding author. E-mail: carsten.henkel@quantum.physik.uni-potsdam.de 相似文献
15.
In this paper, we re-examine a series of gedanken welcher Weg (WW) experiments introduced by Scully, Englert and Walther that contain the essential ideas underlying the quantum eraser. For this purpose we use the Bohm model which gives a sharp picture of the behaviour of the atoms involved in these experiments. This model supports the thesis that interference disappears in such WW experiments, even though the centre of mass wave function remains coherent throughout the experiment. It also shows exactly what it means to say ‘that the interference can be restored by manipulating the WW detectors long after the atoms have passed’. It does not support Wheeler’s notion that ‘the past is undefined and undefinable without the observation (in the present)’. 相似文献
16.
Abhijit Mookerjee 《Pramana》1980,14(1):11-17
A classical Heisen berg model is analysed. The interaction is of the RKKY type and only between sites randomly occupied by
magnetic atoms. The possible phases are described at various temperatures and concentration of magnetic atoms. The procedure
is realistic and not the ‘exactly’ solvable kind studied by earlier workers. 相似文献
17.
We consider the capture of antiprotons with energies less than roughly 27 eV by helium, neon and argon atoms. We use the adiabatic
‘hidden-crossing’ theory to calculate both the capture cross-sections and the angular distribution of the antiprotons. We
find that important differences between helium and the other noble gases can be attributed to the properties of the ‘hidden’
crossings appropriate to each system.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
C. I. Christov 《Foundations of Physics》2010,40(6):575-584
We examine the process of the emission of light from an atom that is in a relative translational motion with respect to the
medium at rest in which the electromagnetic excitations propagate. The effect of Lorentz contraction of the of electron orbits
on the emitted frequency is incorporated in the Rydberg formula, as well as the emitter’s Doppler effect is acknowledged.
The result is that the frequency of the emitted light is modified by a factor that is identical with what is called the ‘relativistic
Doppler effect’. The new emission formula is applied for reinterpretation of the Ives-Stilwell experiment and shown that within
the second order of approximation with respect to the speeds of the atom and the ‘absolute speed’ (Earth’s speed relative
to the medium), the absolute motion does not affect the interference. The expression for the modification of the frequency
involves both a first and a second-order term with respect to the speed of the atoms in the cathode tube. The latter turns
out to be quantitatively the same as if the time would have changed its rate in the frame moving with the atoms. Thus, a new
interpretation of the results of this famous experiment is provided without stipulating time dilation. 相似文献
19.
Summary The data for 3.8 million compounds from structural databases of 32 providers were gathered and stored in a single chemical database. Duplicates are removed using the IUPAC International Chemical Identifier. After this, 2.6 million compounds remain. Each database and the final one were studied in term of uniqueness, diversity, frameworks, ‘drug-like’ and ‘lead–like’ properties. This study also shows that there are more than 87 000 frameworks in the database. It contains 2.1 million ‘drug-like’ molecules among which, more than one million are ‘lead-like’. This study has been carried out using ‘ScreeningAssistant’, a software dedicated to chemical databases management and screening sets generation. Compounds are stored in a MySQL database and all the operations on this database are carried out by Java code. The druglikeness and leadlikeness are estimated with ‘in–house’ scores using functions to estimate convenience to properties; unicity using the InChI code and diversity using molecular frameworks and fingerprints. The software has been conceived in order to facilitate the update of the database. ‘ScreeningAssistant’ is freely available under the GPL license. 相似文献
20.
S. K. Srivastava 《International Journal of Theoretical Physics》2007,46(6):1702-1709
Here, an accelerated phantom model for the late universe is explored, which is free from future singularity. It is interesting
to see that this model exhibits strong curvature for all time in future, unlike models with ‘big-rip singularity’ showing
high curvature near singularity time only. So, quantum gravity effects grow dominant as time increases in late universe too.
More importantly, it is demonstrated that quantum corrections to FRW equations lead to non-violation of ‘cosmic energy conditions’
of general relativity, which are violated for accelerating universe without these corrections. 相似文献