6,972 research outputs found
Accurate measurement of ^{13}C - ^{15}N distances with solid-state NMR
Solid-state NMR technique for measureing distances between hetero-nuclei in
static powder samples is described. It is based on a two-dimensional
single-echo scheme enhanced with adiabatic cross-polarization. As an example,
the results for intra-molecular distances in -crystalline form of
glycine are presented. The measured NMR distances ^13 C(2) - ^15 N and ^13 C(1)
- ^15 N are 1.496 0.002 \AA and 2.50 0.02 \AA, respectively.Comment: 12 page
Quantum information processing using strongly-dipolar coupled nuclear spins
Dipolar coupled homonuclear spins present challenging, yet useful systems for
quantum information processing. In such systems, eigenbasis of the system
Hamiltonian is the appropriate computational basis and coherent control can be
achieved by specially designed strongly modulating pulses. In this letter we
describe the first experimental implementation of the quantum algorithm for
numerical gradient estimation on the eigenbasis of a four spin system.Comment: 5 pages, 5 figures, Accepted in PR
Occult Cerebrovascular Disease and Late-Onset Epilepsy: Could Loss of Neurovascular Unit Integrity Be a Viable Model?
Late-onset epilepsy (LOE) first occurs after 60 years of age and may be due to occult cerebrovascular disease (CVD) which confers an increased risk of stroke. However, patients with late-onset epilepsy are not currently consistently investigated or treated for cerebrovascular risk factors. We discuss how abnormalities of neurovascular unit
function, namely, changes in regional cerebral blood flow and blood brain barrier
disruption, may be caused by occult cerebrovascular disease but present clinically as
late-onset epilepsy. We describe novel magnetic resonance imaging methods to
detect abnormal neurovascular unit function in subjects with LOE and controls. We hypothesise that occult CVD may cause LOE as a result of neurovascular unit dysfunction
Design of Strongly Modulating Pulses to Implement Precise Effective Hamiltonians for Quantum Information Processing
We describe a method for improving coherent control through the use of
detailed knowledge of the system's Hamiltonian. Precise unitary transformations
were obtained by strongly modulating the system's dynamics to average out
unwanted evolution. With the aid of numerical search methods, pulsed
irradiation schemes are obtained that perform accurate, arbitrary, selective
gates on multi-qubit systems. Compared to low power selective pulses, which
cannot average out all unwanted evolution, these pulses are substantially
shorter in time, thereby reducing the effects of relaxation. Liquid-state NMR
techniques on homonuclear spin systems are used to demonstrate the accuracy of
these gates both in simulation and experiment. Simulations of the coherent
evolution of a 3-qubit system show that the control sequences faithfully
implement the unitary operations, typically yielding gate fidelities on the
order of 0.999 and, for some sequences, up to 0.9997. The experimentally
determined density matrices resulting from the application of different control
sequences on a 3-spin system have overlaps of up to 0.99 with the expected
states, confirming the quality of the experimental implementation.Comment: RevTeX3, 11 pages including 2 tables and 5 figures; Journal of
Chemical Physics, in pres
The usefulness of cerebrospinal fluid tests for neurosyphilis
To determine the usefulness of cerebrospinal fluid (CSF) tests for syphilis at a large academic hospital, clinical and laboratory data on 644 patients in whom such testing was requested over a 12-month period were analysed. In 198 cases (31 %) the Treponema paJlidum haemagglutination (TPHA) screening test could not be performed because of insufficient fluid. Thirty-eight of the remaining patients were diagnosed as having active neurosyphilis. Examination of 22 files of patients who had a positive TPHA and fluorescent treponemal antibody absorption (FTA-Abs) test together with a negative CSF Venereal Disease Research Laboratory (VDRL) test revealed that other CSF measures indicating disease activity (CSF protein, cells or IgG index) were not utilised optimally. In 10 (45%) of these patients neurosyphilis was not diagnosed despite either abnormal or incomplete CSF biochemical analysis, indicating that if the CSF VDRL is used as the sole marker for disease activity, some cases of neurosyphilis are likely to be missed
New determination of structure parameters in strong field tunneling ionization theory of molecules
In the strong field molecular tunneling ionization theory of Tong et al.
[Phys. Rev. A 66, 033402 (2002)], the ionization rate depends on the asymptotic
wavefunction of the molecular orbital from which the electron is removed. The
orbital wavefunctions obtained from standard quantum chemistry packages in
general are not good enough in the asymptotic region. Here we construct a
one-electron model potential for several linear molecules using density
functional theory (DFT). We show that the asymptotic wavefunction can be
improved with an iteration method and after one iteration accurate asymptotic
wavefunctions and structure parameters are determined. With the new parameters
we examine the alignment-dependent tunneling ionization probabilities for
several molecules and compare with other calculations and with recent
measurements, including ionization from inner molecular orbitals
Structural and physiological neurovascular changes in idiopathic Parkinson's disease and its clinical phenotypes
Neurovascular changes are likely to interact importantly with the neurodegenerative process in idiopathic Parkinson's disease (IPD). Markers of neurovascular status (NVS) include white matter lesion (WML) burden and arterial spin labelling (ASL) measurements of cerebral blood flow (CBF) and arterial arrival time (AAT). We investigated NVS in IPD, including an analysis of IPD clinical phenotypes, by comparison with two control groups, one with a history of clinical cerebrovascular disease (CVD) (control positive, CP) and one without CVD (control negative, CN). Fifty-one patients with IPD (mean age 69.0 ± 7.7 years) (21 tremor dominant (TD), 24 postural instability and gait disorder (PIGD) and six intermediates), 18 CP (mean age 70.1 ± 8.0 years) and 34 CN subjects (mean age 67.4 ± 7.6 years) completed a 3T MRI scan protocol including T2-weighted fluid-attenuated inversion recovery (FLAIR) and ASL. IPD patients showed diffuse regions of significantly prolonged AAT, small regions of lower CBF and greater WML burden by comparison with CN subjects. TD patients showed lower WML volume by comparison with PIGD patients. These imaging data thus show altered NVS in IPD, with some evidence for IPD phenotype-specific differences
Leucine-rich repeat protein PRAME: expression, potential functions and clinical implications for leukaemia
PRAME/MAPE/OIP4 is a germinal tissue-specific gene that is also expressed at high levels in haematological malignancies and solid tumours. The physiological functions of PRAME in normal and tumour cells are unknown, although a role in the regulation of retinoic acid signalling has been proposed. Sequence homology and structural predictions suggest that PRAME is related to the leucine-rich repeat (LRR) family of proteins, which have diverse functions. Here we review the current knowledge of the structure/function of PRAME and its relevance in leukaemia
“Ah! Our very own Juliet Bravo, or is it Jill Gascoine?” Ashes to Ashes and representations of gender
Thermodynamic aspects of materials' hardness: prediction of novel superhard high-pressure phases
In the present work we have proposed the method that allows one to easily
estimate hardness and bulk modulus of known or hypothetical solid phases from
the data on Gibbs energy of atomization of the elements and corresponding
covalent radii. It has been shown that hardness and bulk moduli of compounds
strongly correlate with their thermodynamic and structural properties. The
proposed method may be used for a large number of compounds with various types
of chemical bonding and structures; moreover, the temperature dependence of
hardness may be calculated, that has been performed for diamond and cubic boron
nitride. The correctness of this approach has been shown for the recently
synthesized superhard diamond-like BC5. It has been predicted that the
hypothetical forms of B2O3, diamond-like boron, BCx and COx, which could be
synthesized at high pressures and temperatures, should have extreme hardness
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