4,230 research outputs found
Universality in edge-source diffusion dynamics
We show that in edge-source diffusion dynamics the integrated concentration
N(t) has a universal dependence with a characteristic time-scale tau=(A/P)^2
pi/(4D), where D is the diffusion constant while A and P are the
cross-sectional area and perimeter of the domain, respectively. For the
short-time dynamics we find a universal square-root asymptotic dependence
N(t)=N0 sqrt(t/tau) while in the long-time dynamics N(t) saturates
exponentially at N0. The exponential saturation is a general feature while the
associated coefficients are weakly geometry dependent.Comment: 4 pages including 4 figures. Minor changes. Accepted for PR
Transport coefficients for electrolytes in arbitrarily shaped nano and micro-fluidic channels
We consider laminar flow of incompressible electrolytes in long, straight
channels driven by pressure and electro-osmosis. We use a Hilbert space
eigenfunction expansion to address the general problem of an arbitrary cross
section and obtain general results in linear-response theory for the hydraulic
and electrical transport coefficients which satisfy Onsager relations. In the
limit of non-overlapping Debye layers the transport coefficients are simply
expressed in terms of parameters of the electrolyte as well as the geometrical
correction factor for the Hagen-Poiseuille part of the problem. In particular,
we consider the limits of thin non-overlapping as well as strongly overlapping
Debye layers, respectively, and calculate the corrections to the hydraulic
resistance due to electro-hydrodynamic interactions.Comment: 13 pages including 4 figures and 1 table. Typos corrected. Accepted
for NJ
Micro- vs. macro-phase separation in binary blends of poly(styrene)-poly(isoprene) and poly(isoprene)-poly(ethylene oxide) diblock copolymers
In this paper we present an experimentally determined phase diagram of binary blends of the diblock copolymers poly(styrene)-poly(isoprene) and poly(isoprene)-poly(ethylene oxide). At high temperatures, the blends form an isotropic mixture. Upon lowering the temperature, the blend macro-phase separates before micro-phase separation occurs. The observed phase diagram is compared to theoretical predictions based on experimental parameters. In the low-temperature phase the crystallisation of the poly(ethylene oxide) block influences the spacing of the ordered phase
Short Bowel Patients Treated for Two Years with Glucagon-Like Peptide 2 (GLP-2): Compliance, Safety, and Effects on Quality of Life
Background and aims. Glucagon-like peptide 2 (GLP-2) has been shown to improve intestinal absorption in short bowel syndrome (SBS) patients in a short-term study. This study describes safety, compliance, and changes in quality of life in 11 SBS patients at baseline, week 13, 26, and 52 during two years of subcutaneous GLP-2 treatment, 400 microgram TID, intermitted by an 8-week washout period.
Methods. Safety and compliance was evaluated during the admissions. The Sickness Impact Profile (SIP), Short Form 36 (SF 36), and Inflammatory Bowel Disease Questionnaire (IBDQ) evaluated quality of life.
Results. The predominant adverse event was transient abdominal discomfort in 5 of 11 patients, but in 2, both suffering from Crohns disease, it progressed to abdominal pain and led to discontinuation of GLP-2 treatment. One had a fibrostenotic lesion electively resected at the jejuno-ascendo-anastomosis. The investigator excluded a patient due to unreliable feedback. Stoma nipple enlargement was seen in all 9 jejunostomy patients. Reported GLP-2 compliance was excellent (>93%). GLP-2 improved the overall quality of life VAS-score (4.1 ± 2.8 cm versus 6.0 ± 2.4 cm, P < .01), the overall SIP score (10.3 ± 8.9% versus 6.2 ± 9.5%, P < .001), the mental component of the SF-36 (45 ± 13% versus 53 ± 11%, P < .05), and the overall IBDQ score (5.1 ± 0.9 versus 5.4 ± 0.9, P < .007) in the 8 patients completing the study.
Conclusions. Long-term treatment with GLP-2 is feasible in SBS patients, although caution must be exercised in patients with a history of abdominal pain. Although conclusions cannot be made in a noncontrolled trial, the high reported compliance might reflect a high treatment satisfaction, where the clinical benefits of GLP-2 may outweigh the discomforts of injections
Short Bowel Patients Treated for Two Years with Glucagon-Like Peptide 2: Effects on Intestinal Morphology and Absorption, Renal Function, Bone and Body Composition, and Muscle Function
Background and aims. In a short-term study, Glucagon-like peptide 2 (GLP-2) has been shown to improve intestinal absorption in short bowel syndrome (SBS) patients. This study describes longitudinal changes in relation to GLP-2 treatment for two years.
Methods. GLP-2, 400 micrograms, s.c.,TID, were offered, to eleven SBS patients keeping parenteral support constant. 72-hour nutritional balance studies were performed at baseline, weeks 13, 26, 52 during two years intermitted by an 8-week washout period. In addition, mucosal morphometrics, renal function (by creatinine clearance), body composition and bone mineral density (by DEXA), biochemical markers of bone turnover (by s-CTX and osteocalcin, PTH and vitamin D), and muscle function (NMR, lungfunction, exercise test) were measured. Results. GLP-2 compliance was >93%. Three of eleven patients did not complete the study. In the remaining 8 patients, GLP-2 significantly reduced the fecal wet weight from approximately 3.0 to approximately 2.0 kg/day. This was accompanied by a decline in the oral wet weight intake, maintaining intestinal wet weight absorption and urinary weight constant. Renal function improved. No significant changes were demonstrated in energy intake or absorption, and GLP-2 did not significantly affect mucosal morphology, body composition, bone mineral density or muscle function. Conclusions. GLP-2 treatment reduces fecal weight by approximately 1000 g/d and enables SBS patients to maintain their intestinal fluid and electrolyte absorption at lower oral intakes. This was accompanied by a 28% improvement in creatinine clearance
Ultra-large bandwidth hollow-core guiding in all-silica Bragg fibers with nano-supports
We demonstrate a new class of hollow-core Bragg fibers that are composed of
concentric cylindrical silica rings separated by nanoscale support bridges. We
theoretically predict and experimentally observe hollow-core confinement over
an octave frequency range. The bandwidth of bandgap guiding in this new class
of Bragg fibers exceeds that of other hollow-core fibers reported in the
literature. With only three rings of silica cladding layers, these Bragg fibers
achieve propagation loss of the order of 1 dB/m.Comment: 9 pages including 5 figure
Structural and evolutionary relationships among protein tyrosine phosphatase domains
With the current access to the whole genomes of various organisms and the completion of the first draft of the human genome, there is a strong need for a structure-function classification of protein families as an initial step in moving from DNA databases to a comprehensive understanding of human biology. As a result of the explosion in nucleic acid sequence information and the concurrent development of methods for high-throughput functional characterization of gene products, the genomic revolution also promises to provide a new paradigm for drug discovery, enabling the identification of molecular drug targets in a significant number of human diseases. This molecular view of diseases has contributed to the importance of combining primary sequence data with three-dimensional structure and has increased the awareness of computational homology modeling and its potential to elucidate protein function. In particular, when important proteins or novel therapeutic targets are identified—like the family of protein tyrosine phosphatases (PTPs) (reviewed in reference 53)—a structure-function classification of such protein families becomes an invaluable framework for further advances in biomedical science. Here, we present a comparative analysis of the structural relationships among vertebrate PTP domains and provide a comprehensive resource for sequence analysis of phosphotyrosine-specific PTPs
Liquid-infiltrated photonic crystals - enhanced light-matter interactions for lab-on-a-chip applications
Optical techniques are finding widespread use in analytical chemistry for
chemical and bio-chemical analysis. During the past decade, there has been an
increasing emphasis on miniaturization of chemical analysis systems and
naturally this has stimulated a large effort in integrating microfluidics and
optics in lab-on-a-chip microsystems. This development is partly defining the
emerging field of optofluidics. Scaling analysis and experiments have
demonstrated the advantage of micro-scale devices over their macroscopic
counterparts for a number of chemical applications. However, from an optical
point of view, miniaturized devices suffer dramatically from the reduced
optical path compared to macroscale experiments, e.g. in a cuvette. Obviously,
the reduced optical path complicates the application of optical techniques in
lab-on-a-chip systems. In this paper we theoretically discuss how a strongly
dispersive photonic crystal environment may be used to enhance the light-matter
interactions, thus potentially compensating for the reduced optical path in
lab-on-a-chip systems. Combining electromagnetic perturbation theory with
full-wave electromagnetic simulations we address the prospects for achieving
slow-light enhancement of Beer-Lambert-Bouguer absorption, photonic band-gap
based refractometry, and high-Q cavity sensing.Comment: Invited paper accepted for the "Optofluidics" special issue to appear
in Microfluidics and Nanofluidics (ed. Prof. David Erickson). 11 pages
including 8 figure
Osteoblast‐Targeted suppression of PPARγ increases osteogenesis through activation of mTOR signaling
Nuclear receptor peroxisome proliferator‐activated receptor‐γ (PPARγ) is an essential transcription factor for adipocyte differentiation. In mesenchymal stem cells, PPARγ has been assumed to play a negative role in osteoblastic differentiation, by working in an adipogenesis dependent manner, due to the reciprocal relationship between osteoblast and adipocyte differentiation. However, the direct role of PPARγ in osteoblast function is not fully understood, due in part to inadequate model systems. Here, we describe an adenoviral‐mediated PPARγ knockout system in which suppression of PPARγ in mesenchymal stem cells enhanced osteoblast differentiation and inhibited adipogenesis in vitro. Consistent with this in vitro observation, lipoatrophic A‐ZIP/F1 mice, which do not form adipocytes, displayed a phenotype in which both cortical and trabecular bone was significantly increased compared with wild‐type mice. We next developed an inducible osteoblast‐targeted PPARγ knockout ( Osx Cre/flox‐ PPARγ ) mouse to determine the direct role of PPARγ in bone formation. Data from both in vitro cultures of mesenchymal stem cells and in vivo µCT analysis of bones suggest that suppression of PPARγ activity in osteoblasts significantly increased osteoblast differentiation and trabecular number. Endogenous PPARγ in mesenchymal stem cells and osteoblasts strongly inhibited Akt/mammalian target of rapamycin (mTOR)/p70S6k activity and led to decreased osteoblastic differentiation. Therefore, we conclude that PPARγ modulates osteoblast differentiation and bone formation through both direct and indirect mechanisms. The direct mode, as shown here, involves PPARγ regulation of the mTOR pathway, while the indirect pathway is dependent on the regulation of adipogenesis. S tem C ells 2013;31:2183–2192Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/100308/1/stem1455.pd
Density functional study of the adsorption and van der Waals binding of aromatic and conjugated compounds on the basal plane of MoS2
Accurate calculations of adsorption energies of cyclic molecules are of key importance in investigations of, e.g., hydrodesulfurization (HDS) catalysis. The present density functional theory (DFT) study of a set of important reactants, products, and inhibitors in HDS catalysis demonstrates that van der Waals interactions are essential for binding energies on MoS2 surfaces and that DFT with a recently developed exchange-correlation functional (vdW-DF) accurately calculates the van der Waals energy. Values are calculated for the adsorption energies of butadiene, thiophene, benzothiophene, pyridine, quinoline, benzene, and naphthalene on the basal plane of MoS2, showing good agreement with available experimental data, and the equilibrium geometry is found as flat at a separation of about 3.5 \uc5 for all studied molecules. This adsorption is found to be due to mainly van der Waals interactions. Furthermore, the manifold of adsorption-energy values allows trend analyses to be made, and they are found to have a linear correlation with the number of main atoms. \ua9 2009 American Institute of Physics
- …