19,594 research outputs found
Crystallization of medium length 1-alcohols in mesoporous silicon: An X-ray diffraction study
The linear 1-alcohols n-C16H33OH, n-C17H35OH, n-C19H37OH have been imbibed
and solidified in lined up, tubular mesopores of silicon with 10 nm and 15 nm
mean diameters, respectively. X-ray diffraction measurements reveal a set of
six discrete orientation states (''domains'') characterized by a perpendicular
alignment of the molecules with respect to the long axis of the pores and by a
four-fold symmetry about this direction, which coincides with the crystalline
symmetry of the Si host. A Bragg peak series characteristic of the formation of
bilayers indicates a lamellar structure of the spatially confined alcohol
crystals in 15 nm pores. By contrast, no layering reflections could be detected
for 10 nm pores. The growth mechanism responsible for the peculiar orientation
states is attributed to a nano-scale version of the Bridgman technique of
single-crystal growth, where the dominant growth direction is aligned
parallelly to the long pore axes. Our observations are analogous to the growth
phenomenology encountered for medium length n-alkanes confined in mesoporous
silicon (Phys. Rev. E 75, 021607 (2007)) and may further elucidate why porous
silicon matrices act as an effective nucleation-inducing material for protein
solution crystallization.Comment: 4 pages, 4 figures, to appear as a Brief Report in Physical Review
Physics Potential of a 2540 Km Baseline Superbeam Experiment
We study the physics potential of a neutrino superbeam experiment with a 2540
km baseline. We assume a neutrino beam similar to the NuMI beam in medium
energy configuration. We consider a 100 kton totally active scintillator
detector at a 7 mr off-axis location. We find that such a configuration has
outstanding hierarchy discriminating capability. In conjunction with the data
from the present reactor neutrino experiments, it can determine the neutrino
mass hierarchy at 3 sigma level in less than 5 years, if sin^2(2*theta13) >
0.01, running in the neutrino mode alone. As a stand alone experiment, with a 5
year neutrino run and a 5 year anti-neutrino run, it can determine non-zero
theta13 at 3 sigma level if sin^2(2*theta13) > 7*10^{-3} and hierarchy at 3
sigma level if sin^2(2*theta13) > 8*10^{-3}. This data can also distinguish
deltaCP = pi/2 from the CP conserving values of 0 and pi, for sin^2(2*theta13)
> 0.02.Comment: 16 pages, 7 figures and 1 table: Published versio
Minimal Neutrino Beta Beam for Large theta_13
We discuss the minimum requirements for a neutrino beta beam if theta_13 is
discovered by an upcoming reactor experiment, such as Double Chooz or Daya Bay.
We require that both neutrino mass hierarchy and leptonic CP violation can be
measured to competitive precisions with a single-baseline experiment in the
entire remaining theta_13 range. We find that for very high isotope production
rates, such as they might be possible using a production ring, a (B,Li) beta
beam with a gamma as low as 60 could already be sufficient to perform all of
these measurements. If only the often used nominal source luminosities can be
achieved, for example, a (Ne,He) beta beam from Fermilab to a possibly existing
water Cherenkov detector at Homestake with gamma \sim 190-350 (depending on the
Double Chooz best-fit) could outperform practically any other beam technology
including wide-band beam and neutrino factory.Comment: 11 pages, 2 figures, 1 tabl
Structural and electronic properties of ScnOm (n=1~3, m=1~2n) clusters: Theoretical study using screened hybrid density functional theory
The structural and electronic properties of small scandium oxide clusters
ScnOm (n = 1 - 3, m = 1 - 2n) are systematically studied within the screened
hybrid density functional theory. It is found that the ground states of these
scandium oxide clusters can be obtained by the sequential oxidation of small
"core" scandium clusters. The fragmentation analysis demonstrates that the ScO,
Sc2O2, Sc2O3, Sc3O3, and Sc3O4 clusters are especially stable. Strong
hybridizations between O-2p and Sc-3d orbitals are found to be the most
significant character around the Fermi level. In comparison with standard
density functional theory calculations, we find that the screened hybrid
density functional theory can correct the wrong symmetries and yield more
precise description for the localized 3d electronic states of scandium.Comment: 8 figure
R2D2 - a symmetric measurement of reactor neutrinos free of systematical errors
We discuss a symmetric setup for a reactor neutrino oscillation experiment
consisting of two reactors separated by about 1 km, and two symmetrically
placed detectors, one close to each reactor. We show that such a configuration
allows a determination of which is essentially free of
systematical errors, if it is possible to separate the contributions of the two
reactors in each detector sufficiently. This can be achieved either by
considering data when in an alternating way only one reactor is running or by
directional sensitivity obtained from the neutron displacement in the detector.Comment: 11 pages, 3 figures, clarifications added, some numbers in relation
with the neutron displacement corrected, version to appear in JHE
Resolving Octant Degeneracy at LBL experiment by combining Daya Bay Reactor Setup
Long baseline Experiment (LBL) have promised to be a very powerful
experimental set up to study various issues related to Neutrinos. Some ongoing
and planned LBL and medium baseline experiments are - T2K, MINOS, NOvA, LBNE,
LBNO etc. But the long baseline experiments are crippled due to presence of
some parameter degeneracies, like the Octant degeneracy. In this work, we first
show the presence of Octant degeneracy in LBL experiments, and then combine it
with Daya Bay Reactor experiment, at different values of CP violation phase. We
show that the Octant degeneracy in LBNE can be resolved completely with this
proposal.Comment: 4 pages, 8 figure
Novel electronic and magnetic properties of BN sheet decorated with hydrogen and fluorine
First principles calculations based on density functional theory reveal some
unusual properties of BN sheet functionalized with hydrogen and fluorine. These
properties differ from those of similarly functionalized graphene even though
both share the same honeycomb structure. (1) Unlike graphene which undergoes a
metal to insulator transition when fully hydrogenated, the band gap of the BN
sheet significantly narrows when fully saturated with hydrogen. Furthermore,
the band gap of the BN sheet can be tuned from 4.7 eV to 0.6 eV and the system
can be a direct or an indirect semiconductor or even a half-metal depending
upon surface coverage. (2) Unlike graphene, BN sheet has hetero-atomic
composition, when co-decorated with H and F, it can lead to anisotropic
structures with rich electronic and magnetic properties. (3) Unlike graphene,
BN sheets can be made ferromagnetic, antiferromagnetic, or magnetically
degenerate depending upon how the surface is functionalized. (4) The stability
of magnetic coupling of functionalized BN sheet can be further modulated by
applying external strain. Our study highlights the potential of functionalized
BN sheets for novel applications.Comment: 18 pages, 6 figures, and 1 tabl
Multi-component symmetry-projected approach for molecular ground state correlations
The symmetry-projected Hartree--Fock ansatz for the electronic structure
problem can efficiently account for static correlation in molecules, yet it is
often unable to describe dynamic correlation in a balanced manner. Here, we
consider a multi-component, systematically-improvable approach, that accounts
for all ground state correlations. Our approach is based on linear combinations
of symmetry-projected configurations built out of a set of non-orthogonal,
variationally optimized determinants. The resulting wavefunction preserves the
symmetries of the original Hamiltonian even though it is written as a
superposition of deformed (broken-symmetry) determinants. We show how short
expansions of this kind can provide a very accurate description of the
electronic structure of simple chemical systems such as the nitrogen and the
water molecules, along the entire dissociation profile. In addition, we apply
this multi-component symmetry-projected approach to provide an accurate
interconversion profile among the peroxo and bis(-oxo) forms of
[CuO], comparable to other state-of-the-art quantum chemical
methods
Molecular effects in the ionization of N, O and F by intense laser fields
In this paper we study the response in time of N, O and F to
laser pulses having a wavelength of 390nm. We find single ionization
suppression in O and its absence in F, in accordance with experimental
results at nm. Within our framework of time-dependent density
functional theory we are able to explain deviations from the predictions of
Intense-Field Many-Body -Matrix Theory (IMST). We confirm the connection of
ionization suppression with destructive interference of outgoing electron waves
from the ionized electron orbital. However, the prediction of ionization
suppression, justified within the IMST approach through the symmetry of the
highest occupied molecular orbital (HOMO), is not reliable since it turns out
that, e.g. in the case of F, the electronic response to the laser pulse is
rather complicated and does not lead to dominant depletion of the HOMO.
Therefore, the symmetry of the HOMO is not sufficient to predict ionization
suppression. However, at least for F, the symmetry of the dominantly
ionized orbital is consistent with the non-suppression of ionization.Comment: 19 pages, 5 figure
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