4,412 research outputs found
Why are Fluid Densities So Low in Carbon Nanotubes?
The equilibrium density of fluids under nanoconfinement can differ
substantially from their bulk density. Using a mean-field approach to describe
the energetic landscape near the carbon nanotube (CNT) wall, we obtain
analytical results describing the lengthscales associated with the layering
observed at the fluid-CNT interface. When combined with molecular simulation
results for the fluid density in the layered region, this approach allows us to
derive a closed-form prediction for the overall equilibrium fluid density as a
function of the CNT radius that is in excellent agreement with molecular
dynamics simulations. We also show how aspects of this theory can be extended
to describe water confined within CNTs and find good agreement with results
from the literature
A Universal Molecular-Kinetic Scaling Relation for Slip of a Simple Fluid at a Solid Boundary
Using the observation that slip in simple fluids at low and moderate shear
rates is a thermally activated process driven by the shear stress in the fluid
close to the solid boundary, we develop a molecular-kinetic model for simple
fluid slip at solid boundaries. The proposed model, which is in the form of a
universal scaling relation that connects slip and shear rate, reduces to the
well known Navier-slip condition under low shear conditions, providing a direct
connection between molecular parameters and the slip length. Molecular-dynamics
simulations are in very good agreement with the predicted dependence of slip on
system parameters, including the temperature and fluid-solid interaction
strength. Connections between our model and previous work, as well as
simulation and experimental results are explored and discussed
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Dietary Supplements: A Historical Examination of its Regulation
The subject of this paper is the regulation of dietary supplements, with the passage of the Dietary Supplement Health and Education Act of 1994 (DSHEA) marked as a turning point. The paper examines the history of regulation prior to DSHEA, and then it proceeds to examine DSHEA itself as legislation. The problems with DSHEA and its enforcement by the Food and Drug Administration (FDA) are then discussed, and I use ephedra as a specific example in illustrating those problems. To complete the examination of the entire regulatory scheme behind dietary supplements, I then address the concurrent regulatory responsibilities that the Federal Trade Commission (FTC) has with the FDA in regulating supplements. As a counterpoint to government regulation, I also examine some areas of products liability law that will be relevant in dietary supplement litigation as an illustration of private regulation via litigation. I conclude the paper by discussing some proposals that can be implemented to improve the dietary supplement regulatory scheme
Mechanical Characterization of Fourth Generation Composite Humerus
Mechanical data on upper extremity surrogate bones, supporting use as biomechanical tools, is limited. The objective of this study was to characterize the structural behaviour of the fourth-generation composite humerus under simulated physiologic bending, specifically, stiffness, rigidity, and mid-diaphysial surface strains. Three humeri were tested in four-point bending, in anatomically defined anteroposterior (AP) and mediolateral (ML) planes. Stiffness and rigidity were derived using loadβdisplacement data. Principal strains were determined at the anterior, posterior, medial, and lateral surfaces in the humeral mid-diaphysial transverse plane of one specimen using stacked rosettes. Linear structural behaviour was observed within the test range. Average stiffness and rigidity were greater in the ML (918βΒ±β18βN/mm; 98.4βΒ±β1.9βNm2) than the AP plane (833βΒ±β16βN/mm; 89.3βΒ±β1.6βNm2), with little inter-specimen variability. The ML/AP rigidity ratio was 1.1. Surface principal strains were similar at the anterior (5.41β¡Ρ/N) and posterior (5.43β¡Ρ/N) gauges for AP bending, and comparatively less for ML bending, i.e. 5.1 and 4.5β¡Ρ/N, at the medial and lateral gauges, respectively. This study provides novel strain and stiffness data for the fourth-generation composite humerus and also adds to published construct rigidity data. The presented results support the use of this composite bone as a tool for modelling and experimentation
Genistein increases epidermal growth factor receptor signaling and promotes tumor progression in advanced human prostate cancer.
Genistein is an isoflavone found in soy, and its chemo-preventive and -therapeutic effects have been well established from in vitro studies. Recently, however, its therapeutic actions in vivo have been questioned due to contradictory reports from animal studies, which rely on rodent models or implantation of cell lines into animals. To clarify in vivo effects of genistein in advanced prostate cancer patients, we developed a patient-derived prostate cancer xenograft model, in which a clinical prostatectomy sample was grafted into immune deficient mice. Our results showed an increased lymph node (LN) and secondary organ metastases in genistein-treated mice compared to untreated controls. Interestingly, invasive malignant cells aggregated to form islands/micrometastasis only in the secondary organs of the genistein-treated groups, not in the untreated control group. To understand the underlying mechanism for metastatic progression, we examined cell proliferation and apoptosis on paraffin-sections. Immunohistological data show that tumors of genistein-treated groups have more proliferating and fewer apoptotic cancer cells than those of the untreated group. Our immunoblotting data suggest that increased proliferation and metastasis are linked to enhanced activities of tyrosine kinases, EGFR and its downstream Src, in genistein-treated groups. Despite the chemopreventive effects proposed by earlier in vitro studies, the cancer promoting effect of genistein observed here suggests the need for careful selection of patients and safer planning of clinical trials
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