21,797 research outputs found
Implications of a DK Molecule at 2.32 GeV
We discuss the implications of a possible quasinuclear DK bound state at 2.32
GeV. Evidence for such a state was recently reported in D_s^+pi^o by the BaBar
Collaboration. We first note that a conventional quark model c-sbar assignment
is implausible, and then consider other options involving multiquark systems.
An I=0 c sbar n nbar baryonium assignment is one possibility. We instead favor
a DK meson molecule assignment, which can account for the mass and quantum
numbers of this state. The higher-mass scalar c-sbar state expected at 2.48 GeV
is predicted to have a very large DK coupling, which would encourage formation
of an I=0 DK molecule. Isospin mixing is expected in hadron molecules, and a
dominantly I=0 DK state with some I=1 admixture could explain both the narrow
total width of the 2.32 GeV state as well as the observed decay to D_s^+ pi^o.
Additional measurements that can be used to test this and related scenarios are
discussed.Comment: 6 pages, 1 figur
Vapor chamber fin studies. Operating characteristics of fin models
Operating characteristics and limits of vapor chamber fins or heat pipe
Safety hazards associated with the charging of lithium/sulfur dioxide cells
A continuing research program to assess the responses of spirally wound, lithium/sulfur dioxide cells to charging as functions of charging current, temperature, and cell condition prior to charging is described. Partially discharged cells that are charged at currents greater than one ampere explode with the time to explosion inversely proportional to the charging current. Cells charged at currents of less than one ampere may fail in one of several modes. The data allows an empirical prediction of when certain cells will fail given a constant charging current
Superconductivity and Cobalt Oxidation State in Metastable Na(x)CoO(2-delta)*yH2O (x ~ 1/3; y ~ 4x)
We report the synthesis and superconducting properties of a metastable form
of the known superconductor NaxCoO2*yH2O (x ~ 1/3, y ~ 4x). Instead of using
the conventional bromine-acetonitrile mixture for sodium deintercalation, we
use an aqueous bromine solution. Using this method, we oxidize the sample to a
point that the sodium cobaltate becomes unstable, leading to formation of other
products if not controlled. This compound has the same structure as the
reported superconductor, yet it exhibits a systematic variation of the
superconducting transition temperature (Tc) as a function of time. Immediately
after synthesis, this compound is not a superconductor, even though it contains
appropriate amounts of sodium and water. The samples become superconducting
with low Tc values after ~ 90 h. Tc continually increases until it reaches a
maximum value (4.5 K) after about 260 h. Then Tc drops drastically, becoming
non-superconducting approximately 100 h later. Corresponding time-dependent
neutron powder diffraction data shows that the changes in superconductivity
exhibited by the metastable cobaltate correspond to slow formation of oxygen
vacancies in the CoO2 layers. In effect, the formation of these defects
continually reduces the cobalt oxidation state causing the sample to evolve
through its superconducting life cycle. Thus, the dome-shaped superconducting
phase diagram is mapped as a function of cobalt oxidation state using a single
sample. The width of this dome based on the formal oxidation state of cobalt is
very narrow - approximately 0.1 valence units wide. Interestingly, the maximum
Tc in NaxCoO2*yH2O occurs when the cobalt oxidation state is near 3.5. Thus, we
speculate that the maximum Tc occurs near the charge ordered insulating state
that correlates with the average cobalt oxidation state of 3.5.Comment: 22 pages, 9 figures, 1 tabl
Shear thickening of cornstarch suspensions as a re-entrant jamming transition
We study the rheology of cornstarch suspensions, a dense system of
non-Brownian particles that exhibits shear thickening, i.e. a viscosity that
increases with increasing shear rate. Using MRI velocimetry we show that the
suspension has a yield stress. From classical rheology it follows that as a
function of the applied stress the suspension is first solid (yield stress),
then liquid and then solid again when it shear thickens. The onset shear rate
for thickening is found to depend on the measurement geometry: the smaller the
gap of the shear cell, the lower the shear rate at which thickening occurs.
Shear thickening can then be interpreted as the consequence of the Reynolds
dilatancy: the system under flow wants to dilate but instead undergoes a
jamming transition because it is confined, as confirmed by measurement of the
dilation of the suspension as a function of the shear rate
Upper and lower bounds on the mean square radius and criteria for occurrence of quantum halo states
In the context of non-relativistic quantum mechanics, we obtain several upper
and lower limits on the mean square radius applicable to systems composed by
two-body bound by a central potential. A lower limit on the mean square radius
is used to obtain a simple criteria for the occurrence of S-wave quantum halo
sates.Comment: 12 pages, 2 figure
Novel highly conductive and transparent graphene based conductors
Future wearable electronics, displays and photovoltaic devices rely on highly
conductive, transparent and yet mechanically flexible materials. Nowadays
indium tin oxide (ITO) is the most wide spread transparent conductor in
optoelectronic applications, however the mechanical rigidity of this material
limits its use for future flexible devices. Here we report novel transparent
conductors based on few layer graphene (FLG) intercalated with ferric chloride
(FeCl3) with an outstandingly high electrical conductivity and optical
transparency. We show that upon intercalation a record low sheet resistance of
8.8 Ohm/square is attained together with an optical transmittance higher than
84% in the visible range. These parameters outperform the best values of ITO
and of other carbon-based materials, making these novel transparent conductors
the best candidates for future flexible optoelectronics
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