196 research outputs found
Non-equilibrium electronic transport in a one-dimensional Mott insulator
We calculate the non-equilibrium electronic transport properties of a
one-dimensional interacting chain at half filling, coupled to non-interacting
leads. The interacting chain is initially in a Mott insulator state that is
driven out of equilibrium by applying a strong bias voltage between the leads.
For bias voltages above a certain threshold we observe the breakdown of the
Mott insulator state and the establishment of a steady-state electronic current
through the system. Based on extensive time-dependent density matrix
renormalization group simulations, we show that this steady-state current
always has the same functional dependence on voltage, independent of the
microscopic details of the model and relate the value of the threshold to the
Lieb-Wu gap. We frame our results in terms of the Landau-Zener dielectric
breakdown picture. Finally, we also discuss the real-time evolution of the
current, and characterize the current-carrying state resulting from the
breakdown of the Mott insulator by computing the double occupancy, the spin
structure factor, and the entanglement entropy.Comment: 12 pages RevTex4, 12 eps figures, as published, minor revision
Transport through quantum dots: A combined DMRG and cluster-embedding study
The numerical analysis of strongly interacting nanostructures requires
powerful techniques. Recently developed methods, such as the time-dependent
density matrix renormalization group (tDMRG) approach or the embedded-cluster
approximation (ECA), rely on the numerical solution of clusters of finite size.
For the interpretation of numerical results, it is therefore crucial to
understand finite-size effects in detail. In this work, we present a careful
finite-size analysis for the examples of one quantum dot, as well as three
serially connected quantum dots. Depending on odd-even effects, physically
quite different results may emerge from clusters that do not differ much in
their size. We provide a solution to a recent controversy over results obtained
with ECA for three quantum dots. In particular, using the optimum clusters
discussed in this paper, the parameter range in which ECA can reliably be
applied is increased, as we show for the case of three quantum dots. As a
practical procedure, we propose that a comparison of results for static
quantities against those of quasi-exact methods, such as the ground-state
density matrix renormalization group (DMRG) method or exact diagonalization,
serves to identify the optimum cluster type. In the examples studied here, we
find that to observe signatures of the Kondo effect in finite systems, the best
clusters involving dots and leads must have a total z-component of the spin
equal to zero.Comment: 16 pages, 14 figures, revised version to appear in Eur. Phys. J. B,
additional reference
Nonlinear Transport through Quantum Dots Studied by the Time-Dependent DMRG
Recent developments on studies of transport through quantum dots obtained by
applying the time-dependent density matrix renormalization group method are
summarized. Some new aspects of Kondo physics which appear in nonequilibrium
steady states are discussed both for the single dot case and for the serially
coupled double-quantum-dot case.Comment: 8 pages, 15 figure
Identification of the initial molecular changes in response to circulating angiogenic cells-mediated therapy in critical limb ischemia
BackgroundCritical limb ischemia (CLI) constitutes the most aggressive form of peripheral arterial occlusive disease, characterized by the blockade of arteries supplying blood to the lower extremities, significantly diminishing oxygen and nutrient supply. CLI patients usually undergo amputation of fingers, feet, or extremities, with a high risk of mortality due to associated comorbidities.Circulating angiogenic cells (CACs), also known as early endothelial progenitor cells, constitute promising candidates for cell therapy in CLI due to their assigned vascular regenerative properties. Preclinical and clinical assays with CACs have shown promising results. A better understanding of how these cells participate in vascular regeneration would significantly help to potentiate their role in revascularization.Herein, we analyzed the initial molecular mechanisms triggered by human CACs after being administered to a murine model of CLI, in order to understand how these cells promote angiogenesis within the ischemic tissues.MethodsBalb-c nude mice (n:24) were distributed in four different groups: healthy controls (C, n:4), shams (SH, n:4), and ischemic mice (after femoral ligation) that received either 50 mu l physiological serum (SC, n:8) or 5x10(5) human CACs (SE, n:8). Ischemic mice were sacrificed on days 2 and 4 (n:4/group/day), and immunohistochemistry assays and qPCR amplification of Alu-human-specific sequences were carried out for cell detection and vascular density measurements. Additionally, a label-free MS-based quantitative approach was performed to identify protein changes related.ResultsAdministration of CACs induced in the ischemic tissues an increase in the number of blood vessels as well as the diameter size compared to ischemic, non-treated mice, although the number of CACs decreased within time. The initial protein changes taking place in response to ischemia and more importantly, right after administration of CACs to CLI mice, are shown.ConclusionsOur results indicate that CACs migrate to the injured area; moreover, they trigger protein changes correlated with cell migration, cell death, angiogenesis, and arteriogenesis in the host. These changes indicate that CACs promote from the beginning an increase in the number of vessels as well as the development of an appropriate vascular network.Institute of Health Carlos III, ISCIII; Junta de Andaluci
Current evidence and future perspectives on HuR and breast cancer development, prognosis, and treatment.
This is the Accepted Manuscript version of the following article, "Ioly Kotta-Loizou, et al., “Current Evidence and Future Perspectives on HuR and Breast Cancer Development, Prognosis, and Treatment”, Neoplasia, Vol. 18(11): 674-688, October 2016." The final published version is available at:https://doi.org/10.1016/j.neo.2016.09.002 Copyright © 2016, Elsevier.Hu-antigen R (HuR) is an RNA-binding posttranscriptional regulator that belongs to the Hu/ELAV family. HuR expression levels are modulated by a variety of proteins, microRNAs, chemical compounds, or the microenvironment, and in turn, HuR affects mRNA stability and translation of various genes implicated in breast cancer formation, progression, metastasis, and treatment. The aim of the present review is to critically summarize the role of HuR in breast cancer development and its potential as a prognosticator and a therapeutic target. In this aspect, all the existing English literature concerning HuR expression and function in breast cancer cell lines, in vivo animal models, and clinical studies is critically presented and summarized. HuR modulates many genes implicated in biological processes crucial for breast cancer formation, growth, and metastasis, whereas the link between HuR and these processes has been demonstrated directly in vitro and in vivo. Additionally, clinical studies reveal that HuR is associated with more aggressive forms of breast cancer and is a putative prognosticator for patients' survival. All the above indicate HuR as a promising drug target for cancer therapy; nevertheless, additional studies are required to fully understand its potential and determine against which types of breast cancer and at which stage of the disease a therapeutic agent targeting HuR would be more effective.Peer reviewedFinal Accepted Versio
Insulated molecular wires: inhibiting orthogonal contacts in metal complex based molecular junctions
Metal complexes are receiving increased attention as molecular wires in fundamental studies of the transport properties of metal|molecule|metal junctions. In this context we report the single-molecule conductance of a systematic series of d8 square-planar platinum(II) trans-bis(alkynyl) complexes with terminal trimethylsilylethynyl (C[triple bond, length as m-dash]CSiMe3) contacting groups, e.g. trans-Pt{C[triple bond, length as m-dash]CC6H4C[triple bond, length as m-dash]CSiMe3}2(PR3)2 (R = Ph or Et), using a combination of scanning tunneling microscopy (STM) experiments in solution and theoretical calculations using density functional theory and non-equilibrium Green's function formalism. The measured conductance values of the complexes (ca. 3–5 × 10−5G0) are commensurate with similarly structured all-organic oligo(phenylene ethynylene) and oligo(yne) compounds. Based on conductance and break-off distance data, we demonstrate that a PPh3 supporting ligand in the platinum complexes can provide an alternative contact point for the STM tip in the molecular junctions, orthogonal to the terminal C[triple bond, length as m-dash]CSiMe3 group. The attachment of hexyloxy side chains to the diethynylbenzene ligands, e.g. trans-Pt{C[triple bond, length as m-dash]CC6H2(Ohex)2C[triple bond, length as m-dash]CSiMe3}2(PPh3)2 (Ohex = OC6H13), hinders contact of the STM tip to the PPh3 groups and effectively insulates the molecule, allowing the conductance through the full length of the backbone to be reliably measured. The use of trialkylphosphine (PEt3), rather than triarylphosphine (PPh3), ancillary ligands at platinum also eliminates these orthogonal contacts. These results have significant implications for the future design of organometallic complexes for studies in molecular junctions
A Negative Feedback Loop That Limits the Ectopic Activation of a Cell Type–Specific Sporulation Sigma Factor of Bacillus subtilis
Two highly similar RNA polymerase sigma subunits, σF and σG, govern the early and late phases of forespore-specific gene expression during spore differentiation in Bacillus subtilis. σF drives synthesis of σG but the latter only becomes active once engulfment of the forespore by the mother cell is completed, its levels rising quickly due to a positive feedback loop. The mechanisms that prevent premature or ectopic activation of σG while discriminating between σF and σG in the forespore are not fully comprehended. Here, we report that the substitution of an asparagine by a glutamic acid at position 45 of σG (N45E) strongly reduced binding by a previously characterized anti-sigma factor, CsfB (also known as Gin), in vitro, and increased the activity of σG in vivo. The N45E mutation caused the appearance of a sub-population of pre-divisional cells with strong activity of σG. CsfB is normally produced in the forespore, under σF control, but sigGN45E mutant cells also expressed csfB and did so in a σG-dependent manner, autonomously from σF. Thus, a negative feedback loop involving CsfB counteracts the positive feedback loop resulting from ectopic σG activity. N45 is invariant in the homologous position of σG orthologues, whereas its functional equivalent in σF proteins, E39, is highly conserved. While CsfB does not bind to wild-type σF, a E39N substitution in σF resulted in efficient binding of CsfB to σF. Moreover, under certain conditions, the E39N alteration strongly restrains the activity of σF in vivo, in a csfB-dependent manner, and the efficiency of sporulation. Therefore, a single amino residue, N45/E39, is sufficient for the ability of CsfB to discriminate between the two forespore-specific sigma factors in B. subtilis
Nutritional value, micronutrient and antioxidant capacity of some green leafy vegetables commonly used by southern coastal people of Bangladesh.
Southern coastal people of Bangladesh are highly vulnerable to food insecurity and malnutrition due to coastal flooding, deforestation and increased soil salinity. A number of green leafy vegetables are found in the southern coastal belt being traditionally eaten as daily basis by local people. But they are unaware of nutritional and medicinal use of these vegetables. To contribute to their wider utilization, five common vegetables namely Hibiscus sabdariffa, Trianthema portulacastrum, Diplazium esculentum, Heliotropium indicum L. and Hygrophila auriculata were selected for analysis of nutritional proximate, micronutrients and antioxidant potential. Nutritional properties were analyzed in terms of moisture, pH, protein, lipid, ash, fibre, minerals and carbohydrate. Total flavonoid, tannin and antioxidant capacity were evaluated using established protocols. The results demonstrated that collected plants are rich in carbohydrate, fibre, proteins, moisture and ash content but low in lipid content. The mineral elements were high with remarkable amount of Na (19.9-21.5 mg/gm), K (7.9-13.5 mg/gm) and P (1.0-1.8 mg/gm). All the samples were found to have considerable amount of flavonoid (90.6-144.5 mg QE/gm) and tannin content (26.8-57.2 mg GAE/gm). The IC50 value of DPPH and superoxide radical scavenging was the lowest for H. indicum (37.1 and 83.4 μg/ml, respectively) whereas T. portulacastrum possessed high reducing power (IC50 53.7 μg/ml). Among the five investigated species, T. portulacastrum and H. indicum were found to have good nutritional and antioxidant properties, thus can be promoted as a significant source of nutritional and antioxidant food supplements
A Mapping of Drug Space from the Viewpoint of Small Molecule Metabolism
Small molecule drugs target many core metabolic enzymes in humans and pathogens,
often mimicking endogenous ligands. The effects may be therapeutic or toxic, but
are frequently unexpected. A large-scale mapping of the intersection between
drugs and metabolism is needed to better guide drug discovery. To map the
intersection between drugs and metabolism, we have grouped drugs and metabolites
by their associated targets and enzymes using ligand-based set signatures
created to quantify their degree of similarity in chemical space. The results
reveal the chemical space that has been explored for metabolic targets, where
successful drugs have been found, and what novel territory remains. To aid other
researchers in their drug discovery efforts, we have created an online resource
of interactive maps linking drugs to metabolism. These maps predict the
“effect space” comprising likely target enzymes for each of
the 246 MDDR drug classes in humans. The online resource also provides
species-specific interactive drug-metabolism maps for each of the 385 model
organisms and pathogens in the BioCyc database collection. Chemical similarity
links between drugs and metabolites predict potential toxicity, suggest routes
of metabolism, and reveal drug polypharmacology. The metabolic maps enable
interactive navigation of the vast biological data on potential metabolic drug
targets and the drug chemistry currently available to prosecute those targets.
Thus, this work provides a large-scale approach to ligand-based prediction of
drug action in small molecule metabolism
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