1,504 research outputs found
Maximally Realistic Causal Quantum Mechanics
We recently constructed a causal quantum mechanics in 2 dim. phase space
which is more realistic than the de Broglie-Bohm mechanics as it reproduces not
just the position but also the momentum probability density of ordinary quantum
theory. Here we present an even more ambitious construction in 2n dim. phase
space. We conjecture that the causal Hamiltonian quantum mechanics presented
here is `maximally realistic'. The positive definite phase space density
reproduces as marginals the correct quantum probability densities of
different complete commuting sets of observables (e.g. , and
other sets). In general the particle velocities do not coincide with the
de Broglie-Bohm velocities.Comment: Published versio
Association between family history and mismatch repair in colorectal cancer
BACKGROUND AND AIMS: Germline mutations in mismatch repair (MMR) genes cause a greatly increased
risk of cancer of the gastrointestinal and female reproductive tracts (hereditary non-polyposis colorectal
cancer (HNPCC)). Loss of MMR expression is common in colorectal cancer (CRC) overall. Such loss is
assumed to be acquired predominantly, although a population of CRC cases will include individuals with
unrecognised MMR mutations. This study examines the association between MMR gene expression and
family history of cancer among the CRC population.
METHODS: Individuals with CRC were identified from two well characterised populations: (1) consecutive
hospital patients (n = 644) and (2) a population based cases series (n = 249). CRC was examined for
expression of hMLH1 and hMSH2 using immunohistochemistry, and expression was related to family history using logistic regression.
RESULTS: hMLH1 and hMSH2 expression was assessed in 732 CRCs with 8% showing loss of expression.
No association was seen overall for hMLH1 or hMSH2 expression and family history of CRC. Loss of
hMSH2 was predicted by family history of extracolonic cancer (odds ratio (OR) 5.78 (95% confidence
interval (CI) 0.95–35.18)) and family history suggestive of HNPCC (OR 27.84 (95% CI 4.37–177.56)).
Loss of hMLH1 was not predicted by family history of extracolonic cancer or a family history suggestive of
HNPCC but was for a family history of at least two affected relatives (OR 4.88 (95% CI 1.25–19.03)).
CONCLUSIONS: Individuals with hMSH2 deficient CRC in the general population exhibit a family history and
other characteristics suggestive of HNPCC, and may carry germline MMR mutations. Loss of hMLH1 is only
associated with a strong family history of extracolonic cancer at older ages, suggesting a novel mechanism
of susceptibility
Bell Inequalities in Phase Space and their Violation in Quantum Mechanics
We derive ``Bell inequalities'' in four dimensional phase space and prove the
following ``three marginal theorem'' for phase space densities
, thus settling a long standing
conjecture : ``there exist quantum states for which more than three of the
quantum probability distributions for , , and
cannot be reproduced as marginals of a positive
''. We also construct the most
general positive which reproduces
any three of the above quantum probability densities for arbitrary quantum
states. This is crucial for the construction of a maximally realistic quantum
theory.Comment: 11 pages, latex, no figure
Uncertainty characteristics of generalized quantum measurements
The effects of any quantum measurement can be described by a collection of
measurement operators {M_m} acting on the quantum state of the measured system.
However, the Hilbert space formalism tends to obscure the relationship between
the measurement results and the physical properties of the measured system. In
this paper, a characterization of measurement operators in terms of measurement
resolution and disturbance is developed. It is then possible to formulate
uncertainty relations for the measurement process that are valid for arbitrary
input states. The motivation of these concepts is explained from a quantum
communication viewpoint. It is shown that the intuitive interpretation of
uncertainty as a relation between measurement resolution and disturbance
provides a valid description of measurement back action. Possible applications
to quantum cryptography, quantum cloning, and teleportation are discussed.Comment: 8 pages, small additions on cloning and on definitions of delta A_mf,
et
Qubits from Number States and Bell Inequalities for Number Measurements
Bell inequalities for number measurements are derived via the observation
that the bits of the number indexing a number state are proper qubits.
Violations of these inequalities are obtained from the output state of the
nondegenerate optical parametric amplifier.Comment: revtex4, 7 pages, v2: results identical but extended presentation,
v3: published versio
Constructing and Characterising Solar Structure Models for Computational Helioseismology
In this paper, we construct background solar models that are stable against
convection, by modifying the vertical pressure gradient of Model S
(Christensen-Dalsgaard et al., 1996, Science, 272, 1286) relinquishing
hydrostatic equilibrium. However, the stabilisation affects the eigenmodes that
we wish to remain as close to Model S as possible. In a bid to recover the
Model S eigenmodes, we choose to make additional corrections to the sound speed
of Model S before stabilisation. No stabilised model can be perfectly
solar-like, so we present three stabilised models with slightly different
eigenmodes. The models are appropriate to study the f and p1 to p4 modes with
spherical harmonic degrees in the range from 400 to 900. Background model CSM
has a modified pressure gradient for stabilisation and has eigenfrequencies
within 2% of Model S. Model CSM_A has an additional 10% increase in sound speed
in the top 1 Mm resulting in eigenfrequencies within 2% of Model S and
eigenfunctions that are, in comparison with CSM, closest to those of Model S.
Model CSM_B has a 3% decrease in sound speed in the top 5 Mm resulting in
eigenfrequencies within 1% of Model S and eigenfunctions that are only
marginally adversely affected. These models are useful to study the interaction
of solar waves with embedded three-dimensional heterogeneities, such as
convective flows and model sunspots. We have also calculated the response of
the stabilised models to excitation by random near-surface sources, using
simulations of the propagation of linear waves. We find that the simulated
power spectra of wave motion are in good agreement with an observed SOHO/MDI
power spectrum. Overall, our convectively stabilised background models provide
a good basis for quantitative numerical local helioseismology. The models are
available for download from http://www.mps.mpg.de/projects/seismo/NA4/.Comment: 35 pages, 23 figures Changed title Updated Figure 1
Deficits in mitochondrial spare respiratory capacity contribute to the neuropsychological changes of alzheimer’s disease
Alzheimer’s disease (AD) is diagnosed using neuropsychological testing, supported by amyloid and tau biomarkers and neuroimaging abnormalities. The cause of neuropsychological changes is not clear since they do not correlate with biomarkers. This study investigated if changes in cellular metabolism in AD correlate with neuropsychological changes. Fibroblasts were taken from 10 AD patients and 10 controls. Metabolic assessment included measuring total cellular ATP, extracellular lactate, mitochondrial membrane potential (MMP), mitochondrial respiration and glycolytic function. All participants were assessed with neuropsychological testing and brain structural MRI. AD patients had significantly lower scores in delayed and immediate recall, semantic memory, phonemic fluency and Mini Mental State Examination (MMSE). AD patients also had significantly smaller left hippocampal, left parietal, right parietal and anterior medial prefrontal cortical grey matter volumes. Fibroblast MMP, mitochondrial spare respiratory capacity (MSRC), glycolytic reserve, and extracellular lactate were found to be lower in AD patients. MSRC/MMP correlated significantly with semantic memory, immediate and delayed episodic recall. Correlations between MSRC and delayed episodic recall remained significant after controlling for age, education and brain reserve. Grey matter volumes did not correlate with MRSC/MMP. AD fibroblast metabolic assessment may represent an emergent disease biomarker of AD
Altered frontal and insular functional connectivity as pivotal mechanisms for apathy in Alzheimer’s disease
Background: Apathy is a common and early symptom in Alzheimer’s disease (AD) and is linked to poorer prognosis. Theoretical interpretations of apathy implicate alterations of connections amongst fronto-striatal and limbic regions.
Objective: To test the association between presence of apathy and patterns of brain functional connectivity in patients with clinically-established AD.
Methods: Seventy AD patients were included. Thirty-five patients experienced apathy as defined by the screening question of the Neuropsychiatric Inventory, and thirty-five did not. All patients agreed to undergo an MRI protocol inclusive of resting-state acquisitions. The hemodynamic-dependent signal was extracted bilaterally from five regions of interest: ventromedial prefrontal cortices, anterior cingulate cortices, dorsolateral prefrontal cortices, insulae and amygdalae. t tests were run to compare connectivity maps of apathetic and non-apathetic patients. Age, education, Mini Mental State Examination score, gray matter volumes and gray matter fractions served as covariates.
Results: At a pFWE < 0.05 threshold, apathetic patients had reduced connectivity between the left insula and right superior parietal cortex. Apathetic patients had also increased connectivity between the right dorsolateral prefrontal seed and the right superior parietal cortex. Patients with apathy were significantly more likely to experience other psychiatric symptoms.
Conclusion: Our findings support a role of frontal and insular connections in coordinating value-based decisions in AD. Both down-regulation and maladaptive up-regulation mechanisms appear to be at play in these regions
Selective biocatalytic hydroxylation of unactivated methylene C-H bonds in cyclic alkyl substrates
The cytochrome P450 monooxygenase CYP101B1 from Novosphingobium aromaticivorans selectively hydroxylated methylene C-H bonds in cycloalkyl rings. Cycloketones and cycloalkyl esters containing C6, C8, C10 and C12 rings were oxidised with high selectively on the opposite side of the ring to the carbonyl substituent. Cyclodecanone was oxidised to oxabicycloundecanol derivatives in equilibrium with the hydroxycyclodecanones.Md Raihan Sarkar, Samrat Dasgupta, Simon M. Pyke and Stephen G. Bel
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