14,246 research outputs found
A kinetic study of the photolysis of tris(2,4-pentanedionato)cobalt(III) and bis(2,4-pentanedionato)cobalt(II) in chloroform
Under 254nm irradiation in chloroform, Co(acac)3 (Hacac = 2,4-pentanedione) is converted to Co(acac)2 and then to CoCl2. The metal complex is the primary photoactive species in the photoreduction of Co(acac)3, but the photosubstitution of Co(acac)2 appears to occur primarily through absorption of light by the solvent, followed by a chain reaction in which chlorine atoms displace pentanedionyl radicals. The photosubstitution rate law is complex, and the apparent quantum yield (based on total light absorbed) varies with incident light intensity and Co(acac)2 concentration, reaching values as high as 16 under the conditions of this study. Referred only to the light absorbed by CHCL3, the highest quantum yield measured was 150. An observed partial inverse dependence of the photosubstitution rate on the initial concentration of Co(acac)2 is explained in terms of a mechanism in which the pentanedione product competes with Co(acac)2 for an intermediate
Drastic Reduction of Shot Noise in Semiconductor Superlattices
We have found experimentally that the shot noise of the tunneling current
through an undoped semiconductor superlattice is reduced with respect to the
Poissonian noise value , and that the noise approaches 1/3 of that value
in superlattices whose quantum wells are strongly coupled. On the other hand,
when the coupling is weak or when a strong electric field is applied to the
superlattice the noise becomes Poissonian. Although our results are
qualitatively consistent with existing theories for one-dimensional mulitple
barriers, the theories cannot account for the dependence of the noise on
superlattice parameters that we have observed.Comment: 4 Pages, 3Figure
Toward an AdS/cold atoms correspondence: a geometric realization of the Schroedinger symmetry
We discuss a realization of the nonrelativistic conformal group (the
Schroedinger group) as the symmetry of a spacetime. We write down a toy model
in which this geometry is a solution to field equations. We discuss various
issues related to nonrelativistic holography. In particular, we argue that free
fermions and fermions at unitarity correspond to the same bulk theory with
different choices for the near-boundary asymptotics corresponding to the source
and the expectation value of one operator. We describe an extended version of
nonrelativistic general coordinate invariance which is realized
holographically.Comment: 14 pages; v2: typos fixed, published versio
Traversable wormhole in the deformed Ho\v{r}ava-Lifshitz gravity
Asymptotically flat wormhole solutions are found in the deformed
Ho\v{r}ava-Lifshitz gravity. It turns out that higher curvature terms can not
play the role of exotic matters which are crucial to form a traversable
wormhole, and external exotic sources are still needed. In particular, the
exotic matter behaves like phantom energy if Kehagias-Sfetsos vacuum is
considered outside the wormhole. Interestingly, the spherically symmetric
setting makes the matter and the higher curvature contribution satisfy
four-dimensional conservation of energy in the covariant form.Comment: 13 pages, 2 figures, version published in Phys. Rev.
Infrared Hall conductivity of NaCoO
We report infrared Hall conductivity of
NaCoO thin films determined from Faraday rotation angle
measurements. exhibits two types of hole
conduction, Drude and incoherent carriers. The coherent Drude carrier shows a
large renormalized mass and Fermi liquid-like behavior of Hall scattering rate,
. The spectral weight is suppressed and disappears at T
= 120K. The incoherent carrier response is centered at mid-IR frequency and
shifts to lower energy with increasing T. Infrared Hall constant is positive
and almost independent of temperature in sharp contrast with the dc-Hall
constant.Comment: 5 Pages, 5 Figures. Author list corrected in metadata only, paper is
unchange
Higgs bosons of a supersymmetric model at the ILC
We study the scalar Higgs sector of the next-to-minimal supersymmetric
standard model with an extra U(1), which has two Higgs doublets and a Higgs
singlet, in the light leptophobic scenario where the extra neutral gauge
boson does not couple to charged leptons. In this model, we find that the
sum of the squared coupling coefficients of the three neutral scalar Higgs
bosons to , normalized by the corresponding SM coupling coefficient is
noticeably smaller than unity, due to the effect of the extra U(1), for a
reasonable parameter space of the model, whereas it is unity in the
next-to-minimal supersymmetric standard model. Thus, these two models may be
distinguished if the coupling coefficients of neutral scalar Higgs bosons to
are measured at the future International Linear Collider by producing them
via the Higgs-strahlung, fusion, and fusion processes.Comment: 12 pages, 2 figures, 1 table, PR
Hydrodynamics with Triangle Anomalies
We consider the hydrodynamic regime of theories with quantum anomalies for
global currents. We show that a hitherto discarded term in the conserve current
is not only allowed by symmetries, but is in fact required by triangle
anomalies and the second law of thermodynamics. This term leads to a number of
new effects, one of which is chiral separation in a rotating fluid at nonzero
chemical potential. The new kinetic coefficients can be expressed, in a unique
fashion, through the anomalies coefficients and the equation of state. We
briefly discuss the relevance of this new hydrodynamic term for physical
situations, including heavy ion collisions.Comment: 4 pages; v2: error in Eq.(4) correcte
Note on two-dimensional gauged Lifshitz models
We fermionize the two-dimensional free Lifshitz scalar field in order to
identify what the gauge covariant couplings are, and then they are bosonized
back to get the gauged Lifshitz scalar field theories. We show that they give
the same physical modes with those of the corresponding Lorentz invariant
gauged scalar theories, although the dispersion relations are different.Comment: 8 pages, to appear in MPL
Reversibility and Improved Hydrogen Release of Magnesium Borohydride
Desorption and subsequent rehydrogenation of Mg(BH_4)_2 with and without 5 mol % TiF_3 and ScCl_3 have been investigated. Temperature programmed desorption (TPD) experiments revealed a significant increase in the rate of desorption as well as the weight percentage of hydrogen released with additives upon heating to 300 °C. Stable Mg(B_xH_y)_n intermediates were formed at 300 °C, whereas MgB_2 was the major product when heated to 600 °C. These samples were then rehydrogenated and subsequently characterized with powder X-ray diffraction (pXRD), Raman, and NMR spectroscopy. We confirmed significant conversion of MgB_2 to fully hydrogenated Mg(BH_4)_2 for the sample with and without additives. TPD and NMR studies revealed that the additives have a significant effect on the reaction pathway during both dehydrogenation and rehydrogenation reactions. This work suggests that the use of additives may provide a valid pathway for improving intrinsic hydrogen storage properties of magnesium borohydride
- …