1,502 research outputs found
Wannier-Stark resonances in optical and semiconductor superlattices
In this work, we discuss the resonance states of a quantum particle in a
periodic potential plus a static force. Originally this problem was formulated
for a crystal electron subject to a static electric field and it is nowadays
known as the Wannier-Stark problem. We describe a novel approach to the
Wannier-Stark problem developed in recent years. This approach allows to
compute the complex energy spectrum of a Wannier-Stark system as the poles of a
rigorously constructed scattering matrix and solves the Wannier-Stark problem
without any approximation. The suggested method is very efficient from the
numerical point of view and has proven to be a powerful analytic tool for
Wannier-Stark resonances appearing in different physical systems such as
optical lattices or semiconductor superlattices.Comment: 94 pages, 41 figures, typos corrected, references adde
Quark model predictions for the SU(6)-breaking ratio of the proton momentum distributions
The ratio between the anomalous magnetic moments of proton and neutron has
been recently parametrized by the ratio of proton momentum fractions
. This ratio is evaluated using different constituent quark
models, starting from the CQM density distributions and calculating the next-to
leading order distributions. We show that this momentum fractions
ratio is a sensitive test for SU(6)-breaking effects and
therefore it is useful to distinguish among different CQMs. We investigate also
the possibility of getting constraints on the formulation of quark structure
models.Comment: 12 pages, 3 figure
Sea-quark flavor asymmetry in the nucleon from a relativistic analysis of the Drell-Yan scattering off nuclei
It is shown that accounting for the relativistic structure of the deuteron
allows to explain the ratio of the Drell-Yan pair production cross-section at
the low Bjorken off the deuteron and the proton. Thus, the sea quark
distributions in the nucleon should be studied with accounting for the effects
of the relativistic structure of the deuteron. The suggested approach reduces
theoretical uncertainty in extracting the ratio from the data
and it is important for the clarification of the nature of the sea quark
asymmetry in the nucleon.Comment: 4 pages, 1 figures, Chiral Symmetry in Hadron and Nuclear Physics
November 13-16, 2007, Osak
Cumulative structure function in terms of nucleonic wave function of the nucleus
The structure function of the nucleus in the cumulative region is
studied in terms of nucleon degrees of freedom. At high the resulting
expressions are presented as a sum of contributions from few-nucleon
correlations. Two-nucleon correlations are studied in some detail. Spin
variables are averaged out. In the region the structure functions are
calculated for the relativistic interaction proposed by F.Gross {\it et al}.
They are found to fall with faster than the exponential. For Carbon at
, where the method is not rigorously applicable, they turn out to be
rougly twice larger than the experimental data.Comment: text and 2 figures in LaTex, 7 figures in P
Substrate-based protein engineering of a flavoprotein oxidase for improved alcohol over-oxidation
The oxidation of alcohols to the corresponding carbonyl compounds represents a convenient strategy for the selective introduction of carbon-acceptor units into carbohydrate-based starting materials from renewable resources. A simple system to accomplish this transformation is by using flavin-containing alcohol oxidases. However, with prim-alcohols, the oxidation does not necessarily stop at the aldehyde stage, but may furnish the carboxylic acid via \u27over\u27-oxidation of the aldehyde hydrate.[1] In order to develop an alcohol oxidase for the efficient transformation of alcohols into carboxylic acids, we chose the recently discovered (5-hydroxymethyl)furfural oxidase (HMFO), which converts not only the eponymous (5-hydroxymethyl)furfural, but also a range of aromatic and allylic alcohols (Figure 1).[2]In order to improve the performance of HMFO for over-oxidation, we anticipated an improved stabilisation of the aldehyde hydrate in the active site to be a crucial factor. After inspection of the HMFO crystal structure, two positions were identified, where hydrogen bond donating and accepting amino acids were introduced, in order to stabilize the gem-diol moiety.[3] Indeed, one of the new HMFO variants exhibited a significantly increased activity for the formation of carboxylic acids from benzylic alcohols.
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2 meg-ampere prototype levitated coil for multipole fusion
The coils major diameter is 1.0 meter and it occupies a cross-section which is about 0.2 meter minor in diameter. The prototype coil will carry four times the current of the largest such magnet built to date. As a result, the peak induction in the coil is about 8 T and the stored magnetic energy will be around 3 MJ. The paper describes the proposed Nb/sub 3/SN superconductor, the quench protection system which is based on the LBL shorted secondary concept, the isochroic refrigeration storage system which stores about 5 kJ of refrigeration between 4.5/sup 0/K and 7/sup 0/K, and the persistent switch
Impact of Motor Therapy with Dynamic Body-Weight Support on Functional Independence Measures in Traumatic Brain Injury: An Exploratory Study
BACKGROUND: Contemporary goals of rehabilitation after traumatic brain injury (TBI) aim to improve cognitive and motor function by applying concepts of neuroplasticity. This can be challenging to carry out in TBI patients with motor, balance, and cognitive impairments.
OBJECTIVE: To determine whether use of dynamic body-weight support (DBWS) would allow safe administration of intensive motor therapy during inpatient rehabilitation and whether its use would yield greater improvement in functional recovery than standard-of-care (SOC) therapy in adults with TBI.
METHODS: Data in this retrospective cohort study was collected from patients with TBI who receive inpatient rehabilitation incorporating DBWS (n = 6) and who received inpatient rehabilitation without DBWS (SOC, n = 6). The primary outcome measure was the change in Functional Independence Measures (FIM) scores from admission to discharge.
RESULTS: There was significant improvement in total FIM scores at discharge compared to admission for both the DBWS (p = 0.001) and SOC (p = 0.005) groups. Overall, the DBWS group had greater improvement in total FIM score and FIM subscales compared to the SOC group.
CONCLUSIONS: Our results suggest DBWS has the potential to allow a greater intensity of therapy during inpatient rehabilitation and yield better outcomes compared to SOC in patients with TBI
Measurement of the Proton Asymmetry Parameter C in Neutron Beta Decay
The proton asymmetry parameter C in neutron decay describes the correlation
between neutron spin and proton momentum. In this Letter, the first measurement
of this quantity is presented. The result C=-0.2377(26) agrees with the
Standard Model expectation. The coefficient C provides an additional parameter
for new and improved Standard Model tests. From a differential analysis of the
same data (assuming the Standard Model), we obtain lambda=-1.275(16) as ratio
of axial-vector and vector coupling constant.Comment: 4 pages, 2 figure
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