169 research outputs found
Kondo effect in quantum dots coupled to ferromagnetic leads with noncollinear magnetizations
Non-equilibrium Green's function technique has been used to calculate
spin-dependent electronic transport through a quantum dot in the Kondo regime.
The dot is described by the Anderson Hamiltonian and is coupled either
symmetrically or asymmetrically to ferromagnetic leads, whose magnetic moments
are noncollinear. It is shown that the splitting of the zero bias Kondo anomaly
in differential conductance decreases monotonically with increasing angle
between magnetizations, and for antiparallel configuration it vanishes in the
symmetrical case while remains finite in the asymmetrical one.Comment: 4 pages, 3 figure
Shale Gas in Poland
An example of interpretation of the Silurian and Ordovician shale formations in the Baltic Basin in Poland regarding determination of potential sweet spots is presented. Short geological information shows the position of shale gas play. Description of the dataâlaboratory measurement outcomes (petrophysical and geochemical) and well loggingâpresents results available for analyses. Detailed elemental analyses and various statistical classifications show the differentiation between sweet spots and adjacent formations. Elastic property modelling based on the known theoretical models and results of comprehensive interpretation of well logs is a good tool to complete information, especially in old wells. Acoustic emission investigations show additional characteristic features of shale gas rock and reveal that acoustic emission and volumetric strain of a shale sample induced by the sorption processes are lower for shale than for coals
Spin effects in single electron tunneling
An important consequence of the discovery of giant magnetoresistance in
metallic magnetic multilayers is a broad interest in spin dependent effects in
electronic transport through magnetic nanostructures. An example of such
systems are tunnel junctions -- single-barrier planar junctions or more complex
ones. In this review we present and discuss recent theoretical results on
electron and spin transport through ferromagnetic mesoscopic junctions
including two or more barriers. Such systems are also called ferromagnetic
single-electron transistors. We start from the situation when the central part
of a device has the form of a magnetic (or nonmagnetic) metallic nanoparticle.
Transport characteristics reveal then single-electron charging effects,
including the Coulomb staircase, Coulomb blockade, and Coulomb oscillations.
Single-electron ferromagnetic transistors based on semiconductor quantum dots
and large molecules (especially carbon nanotubes) are also considered. The main
emphasis is placed on the spin effects due to spin-dependent tunnelling through
the barriers, which gives rise to spin accumulation and tunnel
magnetoresistance. Spin effects also occur in the current-voltage
characteristics, (differential) conductance, shot noise, and others. Transport
characteristics in the two limiting situations of weak and strong coupling are
of particular interest. In the former case we distinguish between the
sequential tunnelling and cotunneling regimes. In the strong coupling regime we
concentrate on the Kondo phenomenon, which in the case of transport through
quantum dots or molecules leads to an enhanced conductance and to a pronounced
zero-bias Kondo peak in the differential conductance.Comment: topical review (36 figures, 65 pages), to be published in J. Phys.:
Condens. Matte
Survey of highly non-Keplerian orbits with low-thrust propulsion
Celestial mechanics has traditionally been concerned with orbital motion under the action of a conservative gravitational potential. In particular, the inverse square gravitational force due to the potential of a uniform, spherical mass leads to a family of conic section orbits, as determined by Isaac Newton, who showed that Keplerâs laws were derivable from his theory of gravitation. While orbital motion under the action of a conservative gravitational potential leads to an array of problems with often complex and interesting solutions, the addition of non-conservative forces offers new avenues of investigation. In particular, non-conservative forces lead to a rich diversity of problems associated with the existence, stability and control of families of highly non-Keplerian orbits generated by a gravitational potential and a non-conservative force. Highly non-Keplerian orbits can potentially have a broad range of practical applications across a number of different disciplines. This review aims to summarize the combined wealth of literature concerned with the dynamics, stability and control of highly non-Keplerian orbits for various low thrust propulsion devices, and to demonstrate some of these potential applications
Frizzled 7 and PIPâ binding by syntenin PDZâ domain supports Frizzled 7 trafficking and signalling
PDZ domain-containing proteins work as intracellular scaffolds to control spatio-temporal aspects of cell signalling. This function is supported by the ability of their PDZ domains to bind other proteins such as receptors, but also phosphoinositide lipids important for membrane trafficking. Here we report a crystal structure of the syntenin PDZ tandem in complex with the carboxy-terminal fragment of Frizzled 7 and phosphatidylinositol 4,5-bisphosphate (PIPâ). The crystal structure reveals a tripartite interaction formed via the second PDZ domain of syntenin. Biophysical and biochemical experiments establish co-operative binding of the tripartite complex and identify residues crucial for membrane PIPâ-specific recognition. Experiments with cells support the importance of the synteninâPIPâ interaction for plasma membrane targeting of Frizzled 7 and c-jun phosphorylation. This study contributes to our understanding of the biology of PDZ proteins as key players in membrane compartmentalization and dynamics
An ultra-deep sequencing strategy to detect sub-clonal TP53 mutations in presentation chronic lymphocytic leukemia cases using multiple polymerases
Chronic lymphocytic leukaemia (CLL) is the most common clonal B-cell disorder characterized by clonal diversity, a relapsing and remitting course, and in its aggressive forms remains largely incurable. Current front-line regimes include agents such as fludarabine, which act primarily via the DNA damage response pathway. Key to this is the transcription factor p53. Mutations in the TP53 gene, altering p53 functionality, are associated with genetic instability, and are present in aggressive CLL. Furthermore, the emergence of clonal TP53 mutations in relapsed CLL, refractory to DNA-damaging therapy, suggests that accurate detection of sub-clonal TP53 mutations prior to and during treatment may be indicative of early relapse. In this study, we describe a novel deep sequencing workflow using multiple polymerases to generate sequencing libraries (MuPol-Seq), facilitating accurate detection of TP53 mutations at a frequency as low as 0.3%, in presentation CLL cases tested. As these mutations were mostly clustered within the regions of TP53 encoding DNA-binding domains, essential for DNA contact and structural architecture, they are likely to be of prognostic relevance in disease progression. The workflow described here has the potential to be implemented routinely to identify rare mutations across a range of diseases
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Ribonucleotide reductase and thymidylate synthase or exogenous deoxyribonucleosides reduce DNA damage and senescence caused by CâMYC depletion
The downâregulation of dominant oncogenes, including CâMYC, in tumor cells often leads to the induction of
senescence via mechanisms that are not completely identified. In the current study, we demonstrate that MYCâdepleted
melanoma cells undergo extensive DNA damage that is caused by the underexpression of thymidylate synthase (TS) and
ribonucleotide reductase (RR) and subsequent depletion of deoxyribonucleoside triphosphate pools. Simultaneous genetic
inhibition of TS and RR in melanoma cells induced DNA damage and senescence phenotypes very similar to the ones
caused by MYCâdepletion. Reciprocally, overexpression of TS and RR in melanoma cells or addition of deoxyribonucleosides
to culture media substantially inhibited DNA damage and senescenceâassociated phenotypes caused by CâMYC
depletion. Our data demonstrate the essential role of TS and RR in CâMYCâdependent suppression of senescence in
melanoma cells.Keywords: ribonucleotide reductase, oncogeneâinduced senescence, dNTP, myc, melanoma, thymidylate synthas
Development of estimates of dietary nitrates, nitrites, and nitrosamines for use with the short willet food frequency questionnaire
<p>Abstract</p> <p>Background</p> <p>Studies have suggested that nitrates, nitrites, and nitrosamines have an etiologic role in adverse pregnancy outcomes and chronic diseases such as cancer. Although an extensive body of literature exists on estimates of these compounds in foods, the extant data varies in quality, quantified estimates, and relevance.</p> <p>Methods</p> <p>We developed estimates of nitrates, nitrites, and nitrosamines for food items listed in the Short Willet Food Frequency Questionnaire (WFFQ) as adapted for use in the National Birth Defects Prevention Study. Multiple reference databases were searched for published literature reflecting nitrate, nitrite, and nitrosamine values in foods. Relevant published literature was reviewed; only publications reporting results for items listed on the WFFQ were selected for inclusion. The references selected were prioritized according to relevance to the U.S. population.</p> <p>Results</p> <p>Based on our estimates, vegetable products contain the highest levels of nitrate, contributing as much as 189 mg/serving. Meat and bean products contain the highest levels of nitrites with values up to 1.84 mg/serving. Alcohol, meat and dairy products contain the highest values of nitrosamines with a maximum value of 0.531 ÎŒg/serving. The estimates of dietary nitrates, nitrites, and nitrosamines generated in this study are based on the published values currently available.</p> <p>Conclusion</p> <p>To our knowledge, these are the only estimates specifically designed for use with the adapted WFFQ and generated to represent food items available to the U.S. population. The estimates provided may be useful in other research studies, specifically in those exploring the relation between exposure to these compounds in foods and adverse health outcomes.</p
Cumulative Prognostic Score Predicting Mortality in Patients Older Than 80 Years Admitted to the ICU.
OBJECTIVES: To develop a scoring system model that predicts mortality within 30âdays of admission of patients older than 80âyears admitted to intensive care units (ICUs). DESIGN: Prospective cohort study. SETTING: A total of 306 ICUs from 24 European countries. PARTICIPANTS: Older adults admitted to European ICUs (Nâ=â3730; median ageâ=â84âyears [interquartile rangeâ=â81-87 y]; 51.8% male). MEASUREMENTS: Overall, 24 variables available during ICU admission were included as potential predictive variables. Multivariable logistic regression was used to identify independent predictors of 30-day mortality. Model sensitivity, specificity, and accuracy were evaluated with receiver operating characteristic curves. RESULTS: The 30-day-mortality was 1562 (41.9%). In multivariable analysis, these variables were selected as independent predictors of mortality: age, sex, ICU admission diagnosis, Clinical Frailty Scale, Sequential Organ Failure Score, invasive mechanical ventilation, and renal replacement therapy. The discrimination, accuracy, and calibration of the model were good: the area under the curve for a score of 10 or higher was .80, and the Brier score was .18. At a cut point of 10 or higher (75% of all patients), the model predicts 30-day mortality in 91.1% of all patients who die. CONCLUSION: A predictive model of cumulative events predicts 30-day mortality in patients older than 80âyears admitted to ICUs. Future studies should include other potential predictor variables including functional status, presence of advance care plans, and assessment of each patient's decision-making capacity
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