排序方式: 共有117条查询结果,搜索用时 281 毫秒
91.
M. P. Lombardo M. L. Paciello S. Petrarca B. Taglienti 《The European Physical Journal C - Particles and Fields》2008,58(1):69-81
We present the first results on scalar glueballs in cold, dense matter using lattice simulations of two-color QCD. The simulations
are carried out on a 63×12 lattice and use a standard hybrid molecular dynamics algorithm for staggered fermions for two values of quark mass. The
glueball correlators are evaluated via a multi-step smearing procedure. The amplitude of the glueball correlator peaks in
correspondence with the zero temperature chiral transition, μ
c=m
π
/2, and the propagators change in a significant way in the superfluid phase, while the Polyakov loop is nearly insensitive
to the transition. Standard analysis suggest that lowest mass in the 0++ gluonic channel decreases in the superfluid phase, but these observations need to be confirmed on larger and more elongated
lattices. These results indicate that a non-zero density induces non-trivial modifications of the gluonic medium. 相似文献
92.
Lowest-lying tetra-quark hadrons in anisotropic lattice QCD 总被引:1,自引:0,他引:1
Mushtaq Loan Zhi-Huan Luo Yu Yiu Lam 《The European Physical Journal C - Particles and Fields》2008,57(3):579-587
We present a detailed study of the lowest-lying
hadrons in quenched improved anisotropic lattice QCD. Using the π
π and diquark–antidiquark local and smeared operators, we attempt to isolate the signal for I(J
P
)=0(0+),2(0+) and 1(1+) states in two flavour QCD. In the chiral limit of the light-quark mass region, the lowest scalar 4q state is found to have a mass, m
4q
I=0=927(12) MeV, which is slightly lower than the experimentally observed f
0(980). The results from our variational analysis do not indicate a signature of a tetraquark resonance in I=1 and I=2 channels. After the chiral extrapolation the lowest 1(1+) state is found to have a mass m
4q
I=1=1358(28) MeV. We analysed the static 4q potential extracted from a tetraquark Wilson loop and illustrated the behaviour of the 4q state as a bound state, unbinding at some critical diquark separation. From our analysis we conclude that the scalar 4q system appears as a two-pion scattering state and that there is no spatially-localised 4q state in the light-quark mass region. 相似文献
93.
Theoretical and interpretative study on the subject of photodetachment of H^- near a partially reflecting surface is presented, and the absorption effect of the surface is investigated on the total and differential cross sections using a theoretical imaging method. To understand the absorption effect, a reflection parameter K is introduced as a multiplicative factor to the outgoing detached-electron wave of H^- propagating towards the wall. The reflection parameter measures, how much electron wave would reflect from the surface; K = 0 corresponds to no reflection and K = 1 corresponds to the total reflection. 相似文献
94.
The lattice QCD studies indicate that the critical temperature T
c ≃ 260-280 MeV of the deconfinement phase transition in quenched QCD is considerably smaller than the lowest-lying glueball
mass m
G ≃ 1500-1700 MeV, i.e., T
c ≪ m
G. As a consequence of this large difference, the thermal excitation of the glueball in the confinement phase is strongly suppressed
by the statistical factor e
-mG/Tc ≃ 0.00207 even near T ≃ T
c. We consider its physical implication, and argue the abnormal feature of the deconfinement phase transition in quenched QCD
from the statistical viewpoint. To appreciate this, we demonstrate a statistical argument of the QCD phase transition using
the recent lattice QCD data. From the phenomenological relation between T
c and the glueball mass, the deconfinement transition is found to take place in quenched QCD before a reasonable amount of
glueballs is thermally excited. In this way, quenched QCD reveals a question “what is the trigger of the deconfinement phase
transition ?”
Received: 18 November 2002 / Accepted: 4 February 2003 / Published online: 29 April 2003 相似文献
95.
Amorphous gallium nitride (a-GaN) films have been deposited on Si (100) substrates using ion-assisted deposition. The deposited films were characterised by X-ray diffraction (XRD) and atomic force microscopy (AFM). XRD confirms the amorphous nature of the films and AFM showed nanostructures in the films. The field electron emission from the film was obtained in a probe-hole field emission microscope, and the current-voltage (I-V) characteristics were studied. The corresponding Fowler-Nordheim (F-N) plots showed a linear behaviour. A current density of 0.1 A/cm2 has been obtained for 1.2 V/μm electric field. The field emission current-time (I-t), curves were recorded at a current level of 500 nA for 3 h. The field emission behaviour is compared with that of crystalline GaN as reported in literature. 相似文献
96.
Thin films of amorphous indium selenide compounds (a-InxSe1−x) are important, e.g. for photovoltaics. The feature of merit in such applications is also the real part of refractive index n of this material. The data on n in literature are divergent. In this paper, the results of investigations on n in the bulk as well as in the interface layers of thin films of a-InxSe1−x are presented. The measurements had been performed using optical transmittance and reflectance in spectral range from 1.24 to 1.96 eV of linear polarized radiation that hit the samples with angles of incidence from 0° to 80°. Investigations had been done for sample temperatures from 80 to 340 K. It was found that the refractive index for areas at the free surface nf is bigger than the refractive index nb at the interface of thin film-substrate. The averaged over thin film thickness value of real part refractive index have the biggest value in all spectral range. Values of these coefficients increase with increasing the temperature. 相似文献
97.
In a wind-blown sand layer, it has been found that wind transport of
particles is always associated with separation of electric charge. This
electrification in turn produces some electrostatic forces in addition to
the gravitational and fluid friction forces that affect the movement of
saltating sand particles, further, the wind-blown sand saltation. To
evaluate this effect quantitatively, this paper presents a simulation of
evolution of wind-blown sand grains after the electrostatic forces exerted
on the grains are taken into account in the wind feedback mechanism of
wind-blown saltation. That is, the coupling interaction between the wind
flow and the saltating sand particles is employed in the simulation to the
non-stationary wind and sand flows when considering fluid drag, gravitation,
and a kind of electrostatic force generated from a distribution of electric
field changing with time in the evolution process of the sand saltation. On
the basis of the proposed simulation model, a numerical program is given to
perform the simulation of this dynamic process and some characteristic
quantities, e.g., duration of the system to reach the steady state, and
curves of the saltating grain number, grain transport rate, mass-flux
profile, and wind profile varying with time during the non-stationary
evolution are displayed. The obtained numerical results exhibit that the
electrostatic force is closely related to the average charge-to-mass ratio
of sand particles and has obvious influence on these characteristic
quantities. The obtained results also show that the duration of the system
to reach the steady state, the sand transport rate and the mass flux profile
coincide well with experimental results by Shao and Raupach (1992) when the
average charge-to-mass ratio of sand particles is 60 μC/kg for the sand
particles with average diameter of 0.25 mm. When the average charge-to-mass
ratios of sand particles are taken as some other certain values, the
calculation results still show that the mass flux profiles are well in
agreement with the experimental data by Rasmussen and Mikkelsen (1998) for
another category of sand particles, which tell us that the electrostatic
force is one of main factors that have to be considered in the research of
mechanism of wind-blown sand saltation. 相似文献
98.
Li Wang Sima Dimitrijev Jisheng Han Francesca Iacopi Jin Zou 《Journal of Crystal Growth》2009,311(19):4442-4446
This paper presents a study of the transition between amorphous and crystalline phases of SiC films deposited on Si(1 0 0) substrate using H3SiCH3 as a single precursor by a conventional low-pressure chemical vapor deposition method in a hot-wall reactor. The microstructure of SiC, characterized by X-ray diffraction and high-resolution transmission electron microscopy, is found to vary with substrate temperature and H3SiCH3 pressure. The grain size decreases with increasing MS pressure at a given temperature and also decreases with reducing temperature at a given MS pressure. The deposition rates are exponentially dependent on the substrate temperature with the activation energy of around 2.6 eV. The hydrogen compositional concentration in the deposited SiC films, determined by secondary ion mass spectrometry depth profiling, is only 2.9% in the nanocrystalline SiC but more than 10% in the amorphous SiC, decreasing greatly with increasing deposition temperature. No hydride bonds are detected by Fourier transform infrared spectroscopy measurements. The chemical order of the deposited SiC films improves with increasing deposition temperature. 相似文献
99.
Optical and Electrical Properties Evolution of Diamond-Like Carbon Thin Films with Deposition Temperature
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Optical and electrical properties of diamond-like carbon (DLC) films deposited by pulsed laser ablation of graphite target at different substrate temperatures are reported. By varying the deposition temperature from 400 to 25℃, the film optical transparency and electrical resistivity increase severely. Most importantly, the transparency and resistivity properties of the DLC films can be tailored to approaching diamond by adjusting the deposition temperature, which is critical to many applications. DLC films deposited at low temperatures show excellent optical transmittance and high resistivity. Over the same temperature regime an increase of the spa bonded C content is observed using visible Raman spectroscopy, which is responsible for the enhanced transparency and resistivity properties. 相似文献
100.
Simulation of SET Operation in Phase-Change Random Access Memories with Heater Addition and Ring-Type Contactor for Low-Power Consumption by Finite Element Modeling
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A three-dimensional finite element model for phase change random access memory (PCRAM) is established for comprehensive electrical and thermal analysis during SET operation. The SET behaviours of the heater addition structure (HS) and the ring-type contact in bottom electrode (RIB) structure are compared with each other. There are two ways to reduce the RESET current, applying a high resistivity interracial layer and building a new device structure. The simulation resuIts indicate that the variation of SET current with different power reduction ways is little. This study takes the RESET and SET operation current into consideration, showing that the RIB structure PCRAM cell is suitable for future devices with high heat efficiency and high-density, due to its high heat efficiency in RESET operation. 相似文献