779 research outputs found
Average Yarding Distance for Row Thinning of Plantations
An average yarding distance model for rectilinear skidtrail layout from a centralized landing is given. The model is appropriate to the evaluation of some row thinning designs in plantations. The theoretical basis for formulas used in the model is briefly described. The model was coded for computer solution and applied to a hypothetical example the results of which are presented
Particle interactions and lattice dynamics: Scenarios for efficient bidirectional stochastic transport?
Intracellular transport processes driven by molecular motors can be described
by stochastic lattice models of self-driven particles. Here we focus on
bidirectional transport models excluding the exchange of particles on the same
track. We explore the possibility to have efficient transport in these systems.
One possibility would be to have appropriate interactions between the various
motors' species, so as to form lanes. However, we show that the lane formation
mechanism based on modified attachment/detachment rates as it was proposed
previously is not necessarily connected to an efficient transport state and is
suppressed when the diffusivity of unbound particles is finite. We propose
another interaction mechanism based on obstacle avoidance that allows to have
lane formation for limited diffusion. Besides, we had shown in a separate paper
that the dynamics of the lattice itself could be a key ingredient for the
efficiency of bidirectional transport. Here we show that lattice dynamics and
interactions can both contribute in a cooperative way to the efficiency of
transport. In particular, lattice dynamics can decrease the interaction
threshold beyond which lanes form. Lattice dynamics may also enhance the
transport capacity of the system even when lane formation is suppressed.Comment: 25 pages, 17 figures, 2 table
Validation of DNA probes for molecular cytogenetics by mapping onto immobilized circular DNA
<p>Abstract</p> <p>Background</p> <p>Fluorescence <it>in situ </it>hybridization (FISH) is a sensitive and rapid procedure to detect gene rearrangements in tumor cells using non-isotopically labeled DNA probes. Large insert recombinant DNA clones such as bacterial artificial chromosome (BAC) or P1/PAC clones have established themselves in recent years as preferred starting material for probe preparations due to their low rates of chimerism and ease of use. However, when developing probes for the quantitative analysis of rearrangements involving genomic intervals of less than 100 kb, careful probe selection and characterization are of paramount importance.</p> <p>Results</p> <p>We describe a sensitive approach to quality control probe clones suspected of carrying deletions or for measuring clone overlap with near kilobase resolution. The method takes advantage of the fact that P1/PAC/BAC's can be isolated as circular DNA molecules, stretched out on glass slides and fine-mapped by multicolor hybridization with smaller probe molecules. Two examples demonstrate the application of this technique: mapping of a gene-specific ~6 kb plasmid onto an unusually small, ~55 kb circular P1 molecule and the determination of the extent of overlap between P1 molecules homologous to the human NF-κB2 locus.</p> <p>Conclusion</p> <p>The relatively simple method presented here does not require specialized equipment and may thus find widespread applications in DNA probe preparation and characterization, the assembly of physical maps for model organisms or in studies on gene rearrangements.</p
Mutational pathway determines whether drug gradients accelerate evolution of drug-resistant cells
Drug gradients are believed to play an important role in the evolution of
bacteria resistant to antibiotics and tumors resistant to anti-cancer drugs. We
use a statistical physics model to study the evolution of a population of
malignant cells exposed to drug gradients, where drug resistance emerges via a
mutational pathway involving multiple mutations. We show that a non-uniform
drug distribution has the potential to accelerate the emergence of resistance
when the mutational pathway involves a long sequence of mutants with increasing
resistance, but if the pathway is short or crosses a fitness valley, the
evolution of resistance may actually be slowed down by drug gradients. These
predictions can be verified experimentally, and may help to improve strategies
for combatting the emergence of resistance.Comment: 6 pages, 3 figures, final version before acceptance to Phys. Rev.
Letters. P.G and B.W contributed equally to this wor
Inhibition of EGFR Signaling: All Mutations Are Not Created Equal
Gazdar and Minna discuss the context and implications of a research article that examines the transformation potential and response to inhibitors of specific EGFR mutations found in lung cancer
Cardiovascular risk in patients with alpha-1-antitrypsin deficiency
Background: Alpha-1-antitrypsin deficiency (AATD) is a rare inherited condition caused by mutations of the SERPINA1
gene that is associated with the development of a COPD like lung disease. The comorbidities in patients with AATDrelated lung diseases are not well defined. The aim of this study was to analyze the clinical phenotype of AATD
patients within the German COPD cohort study COSYCONET (“COPD and SYstemic consequences-COmorbidities
NETwork”) cohort focusing on the distribution of comorbidities.
Method and results: The data from 2645 COSYCONET patients, including 139 AATD patients (110 with and 29 without
augmentation therapy), were analyzed by descriptive statistics and regression analyses. We found significantly lower
prevalence of cardiovascular comorbidities in AATD patients as compared to non-AATD COPD patients. After correction
for age, pack years, body mass index, and sex, the differences were still significant for coronary artery disease (p = 0.002)
and the prevalence of peripheral artery disease as determined by an ankle-brachial-index <= 0.9 (p = 0.035). Also the
distribution of other comorbidities such as bronchiectasis differed between AATD and non-deficient COPD.
Conclusion: AATD is associated with a lower prevalence of cardiovascular disease, the underlying mechanisms need
further investigation
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β-glucan-dependent shuttling of conidia from neutrophils to macrophages occurs during fungal infection establishment
The initial host response to fungal pathogen invasion is critical to infection establishment and outcome. However, the diversity of leukocyte-pathogen interactions is only recently being appreciated. We describe a new form of interleukocyte conidial exchange called "shuttling." In Talaromyces marneffei and Aspergillus fumigatus zebrafish in vivo infections, live imaging demonstrated conidia initially phagocytosed by neutrophils were transferred to macrophages. Shuttling is unidirectional, not a chance event, and involves alterations of phagocyte mobility, intercellular tethering, and phagosome transfer. Shuttling kinetics were fungal-species-specific, implicating a fungal determinant. β-glucan serves as a fungal-derived signal sufficient for shuttling. Murine phagocytes also shuttled in vitro. The impact of shuttling for microbiological outcomes of in vivo infections is difficult to specifically assess experimentally, but for these two pathogens, shuttling augments initial conidial redistribution away from fungicidal neutrophils into the favorable macrophage intracellular niche. Shuttling is a frequent host-pathogen interaction contributing to fungal infection establishment patterns
Cardiovascular risk in patients with alpha-1-antitrypsin deficiency
Background: Alpha-1-antitrypsin deficiency (AATD) is a rare inherited condition caused by mutations of the SERPINA1 gene that is associated with the development of a COPD like lung disease. The comorbidities in patients with AATD-related lung diseases are not well defined. The aim of this study was to analyze the clinical phenotype of AATD patients within the German COPD cohort study COSYCONET (“COPD and SYstemic consequences-COmorbidities NETwork”) cohort focusing on the distribution of comorbidities. Method and results: The data from 2645 COSYCONET patients, including 139 AATD patients (110 with and 29 without augmentation therapy), were analyzed by descriptive statistics and regression analyses. We found significantly lower prevalence of cardiovascular comorbidities in AATD patients as compared to non-AATD COPD patients. After correction for age, pack years, body mass index, and sex, the differences were still significant for coronary artery disease (p = 0.002) and the prevalence of peripheral artery disease as determined by an ankle-brachial-index <= 0.9 (p = 0.035). Also the distribution of other comorbidities such as bronchiectasis differed between AATD and non-deficient COPD. Conclusion: AATD is associated with a lower prevalence of cardiovascular disease, the underlying mechanisms need further investigation
Structure of the silicon vacancy in 6H-SiC after annealing identified as the carbon vacancy–carbon antisite pair
We investigated radiation-induced defects in neutron-irradiated and subsequently annealed 6H-silicon carbide (SiC) with electron paramagnetic resonance (EPR), the magnetic circular dichroism of the absorption (MCDA), and MCDA-detected EPR (MCDA-EPR). In samples annealed beyond the annealing temperature of the isolated silicon vacancy we observed photoinduced EPR spectra of spin S=1 centers that occur in orientations expected for nearest neighbor pair defects. EPR spectra of the defect on the three inequivalent lattice sites were resolved and attributed to optical transitions between photon energies of 999 and 1075 meV by MCDA-EPR. The resolved hyperfine structure indicates the presence of one single carbon nucleus and several silicon ligand nuclei. These experimental findings are interpreted with help of total energy and spin density data obtained from the standard local-spin density approximation of the density-functional theory, using relaxed defect geometries obtained from the self-consistent charge density-functional theory based tight binding scheme. We have checked several defect models of which only the photoexcited spin triplet state of the carbon antisite–carbon vacancy pair (CSi-VC) in the doubly positive charge state can explain all experimental findings. We propose that the (CSi-VC) defect is formed from the isolated silicon vacancy as an annealing product by the movement of a carbon neighbor into the vacancy
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