1,993 research outputs found
Two-photon photoassociation spectroscopy of CsYb: Ground-state interaction potential and interspecies scattering lengths
We perform two-photon photoassociation spectroscopy of the heteronuclear CsYb molecule to measure the binding energies of near-threshold vibrational levels of the X 2+ 1/2 molecular ground state. We report results for 133Cs170Yb, 133Cs173Yb, and 133Cs174Yb, in each case determining the energy of several vibrational levels including the least-bound state. We fit an interaction potential based on electronic structure calculations to the binding energies for all three isotopologs and find that the ground-state potential supports 77 vibrational levels. We use the fitted potential to predict the interspecies s-wave scattering lengths for all seven Cs+Yb isotopic mixtures
Mass formulas and thermodynamic treatment in the mass-density-dependent model of strange quark matter
The previous treatments for strange quark matter in the quark
mass-density-dependent model have unreasonable vacuum limits. We provide a
method to obtain the quark mass parametrizations and give a self-consistent
thermodynamic treatment which includes the MIT bag model as an extreme. In this
treatment, strange quark matter in bulk still has the possibility of absolute
stability. However, the lower density behavior of the sound velocity is
opposite to previous findings.Comment: Formatted in REVTeX 3.1, 5 pages, 3 figures, to appear in PRC6
The Abundance of New Kind of Dark Matter Structures
A new kind of dark matter structures, ultracompact minihalos (UCMHs) was
proposed recently. They would be formed during the radiation dominated epoch if
the large density perturbations are existent. Moreover, if the dark matter is
made up of weakly interacting massive particles, the UCMHs can have effect on
cosmological evolution because of the high density and dark matter annihilation
within them. In this paper, one new parameter is introduced to consider the
contributions of UCMHs due to the dark matter annihilation to the evolution of
cosmology, and we use the current and future CMB observations to obtain the
constraint on the new parameter and then the abundance of UCMHs. The final
results are applicable for a wider range of dark matter parametersComment: 4 pages, 1 tabl
Decoherence in elastic and polaronic transport via discrete quantum states
Here we study the effect of decoherence on elastic and polaronic transport
via discrete quantum states. The calculations are performed with the help of
nonperturbative computational scheme, based on the Green's function theory
within the framework of polaron transformation (GFT-PT), where the many-body
electron-phonon interaction problem is mapped exactly into a single-electron
multi-channel scattering problem. In particular, the influence of dephasing and
relaxation processes on the shape of the electrical current and shot noise
curves is discussed in detail under the linear and nonlinear transport
conditions.Comment: 11 pages, 3 figure
Pentacene islands grown on ultra-thin SiO2
Ultra-thin oxide (UTO) films were grown on Si(111) in ultrahigh vacuum at
room temperature and characterized by scanning tunneling microscopy. The
ultra-thin oxide films were then used as substrates for room temperature growth
of pentacene. The apparent height of the first layer is 1.57 +/- 0.05 nm,
indicating standing up pentacene grains in the thin-film phase were formed.
Pentacene is molecularly resolved in the second and subsequent molecular
layers. The measured in-plane unit cell for the pentacene (001) plane (ab
plane) is a=0.76+/-0.01 nm, b=0.59+/-0.01 nm, and gamma=87.5+/-0.4 degrees. The
films are unperturbed by the UTO's short-range spatial variation in tunneling
probability, and reduce its corresponding effective roughness and correlation
exponent with increasing thickness. The pentacene surface morphology follows
that of the UTO substrate, preserving step structure, the long range surface
rms roughness of ~0.1 nm, and the structural correlation exponent of ~1.Comment: 15 pages, 4 figure
Wedgebox analysis of four-lepton events from neutralino pair production at the LHC
`Wedgebox' plots constructed by plotting the di-electron invariant mass
versus the di-muon invariant mass from pp -> e^+e^- mu^+ mu^- + missing energy
signature LHC events. Data sets of such events are obtained across the MSSM
input parameter space in event-generator simulations, including cuts designed
to remove SM backgrounds. Their study reveals several general features:
(1)Regions in the MSSM input parameter space where a sufficient number of
events are expected so as to be able to construct a clear wedgebox plot are
delineated. (2)The presence of box shapes on a wedgebox plot either indicates
the presence of heavy Higgs bosons decays or restricts the location to a quite
small region of low \mu and M_2 values \lsim 200 GeV, a region denoted as the
`lower island'. In this region, wedgebox plots can be quite complicated and
change in pattern rather quickly as one moves around in the (\mu, M_2) plane.
(3)Direct neutralino pair production from an intermediate Z^{0*} may only
produce a wedge-shape since only \widetilde{\chi}_2^0\widetilde{\chi}_3^0
decays can contribute significantly. (4)A double-wedge or
wedge-protruding-from-a-box pattern on a wedgebox plot, which results from
combining a variety of MSSM production processes, yields three distinct
observed endpoints, almost always attributable to \widetilde{\chi}_{2,3,4}^0
\to \widetilde{\chi}_1^0 \ell^+\ell^- decays, which can be utilized to
determine a great deal of information about the neutralino and slepton mass
spectra and related MSSM input parameters. Wedge and double-wedge patterns are
seen in wedgebox plots in another region of higher \mu and M_2 values, denoted
as the`upper island.' Here the pattern is simpler and more stable as one moves
across the (\mu, M_2) input parameter space.Comment: 28 pages (LaTeX), 8 figures (encapsulated postscript
A Nonlinear Force-Free Magnetic Field Approximation Suitable for Fast Forward-Fitting to Coronal Loops. II. Numeric Code and Tests
Based on a second-order approximation of nonlinear force-free magnetic field
solutions in terms of uniformly twisted field lines derived in Paper I, we
develop here a numeric code that is capable to forward-fit such analytical
solutions to arbitrary magnetogram (or vector magnetograph) data combined with
(stereoscopically triangulated) coronal loop 3D coordinates. We test the code
here by forward-fitting to six potential field and six nonpotential field cases
simulated with our analytical model, as well as by forward-fitting to an
exactly force-free solution of the Low and Lou (1990) model. The
forward-fitting tests demonstrate: (i) a satisfactory convergence behavior
(with typical misalignment angles of ), (ii)
relatively fast computation times (from seconds to a few minutes), and (iii)
the high fidelity of retrieved force-free -parameters ( for simulations and for the Low and Lou model). The
salient feature of this numeric code is the relatively fast computation of a
quasi-forcefree magnetic field, which closely matches the geometry of coronal
loops in active regions, and complements the existing {\sl nonlinear force-free
field (NLFFF)} codes based on photospheric magnetograms without coronal
constraints.Comment: Solar PHysics, (in press), 25 pages, 11 figure
The role of interparticle heterogeneities in the selenization pathway of Cu Zn Sn S nanoparticle thin films a real time study
Real time energy dispersive X ray diffraction EDXRD analysis has been utilized to observe the selenization of Cu Zn Sn S nanoparticle films coated from three nanoparticle populations Cu and Sn rich particles roughly 5 nm in size, Zn rich nanoparticles ranging from 10 to 20 nm in diameter, and a mixture of both types of nanoparticles roughly 1 1 by mass , which corresponds to a synthesis recipe yielding CZTSSe solar cells with reported total area efficiencies as high as 7.9 . The EDXRD studies presented herein show that the formation of copper selenide intermediates during the selenization of mixed particle films can be primarily attributed to the small, Cu and Sn rich particles. Moreover, the formation of these copper selenide phases represents the first stage of the CZTSSe grain growth mechanism. The large, Zn rich particles subsequently contribute their composition to form micrometer sized CZTSSe grains. These findings enable further development of a previously proposed selenization pathway to account for the roles of interparticle heterogeneities, which in turn provides a valuable guide for future optimization of processes to synthesize high quality CZTSSe absorber layer
Large-area freestanding gold nanomembranes with nanoholes
Thin metal films with nanohole arrays have opened up new opportunities in applications ranging from plasmonics to optoelectronics. However, their dependence on substrates limits not only their performance but also other application possibilities. A key challenge to overcome this limitation is to make these nanostructured films substrate-free. Here we report large-area freestanding gold nanomembranes with nanohole arrays fabricated using a replication-releasing procedure. The structures maintain spatial uniformity and pristine quality after release across the entire membrane up to 75 cm2 in area and as thin as 50 nm. The freestanding nanomembranes show significantly enhanced optical transmission and effective field extension compared to the same nanomembranes on substrates. A plasmonic coupling resonance with a 2.7 nm linewidth achieves a record figure-of-merit of 240 for refractive index sensing. The gold nanomembranes can be geometrically converted to 3D microstructures by ion-irradiation-based kirigami technique. The transformed micro-objects can be precisely controlled via geometry design and strategic cutting. Furthermore, we find the presence of nanoholes can significantly change the in-plane modulus of the gold nanomembranes. Finally, the freestanding gold nanomembranes can be transferred to non-planar substrates, enabling their future integration with advanced optical and electronic systems for emerging applications.Peipei Jia, Kamil Zuber, Qiuquan Guo, Brant C. Gibson, Jun Yang and Heike Ebendorff-Heideprie
Chaotic memristor
We suggest and experimentally demonstrate a chaotic memory resistor
(memristor). The core of our approach is to use a resistive system whose
equations of motion for its internal state variables are similar to those
describing a particle in a multi-well potential. Using a memristor emulator,
the chaotic memristor is realized and its chaotic properties are measured. A
Poincar\'{e} plot showing chaos is presented for a simple nonautonomous circuit
involving only a voltage source directly connected in series to a memristor and
a standard resistor. We also explore theoretically some details of this system,
plotting the attractor and calculating Lyapunov exponents. The multi-well
potential used resembles that of many nanoscale memristive devices, suggesting
the possibility of chaotic dynamics in other existing memristive systems.Comment: Applied Physics A (in press
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