2,024 research outputs found
Shear-dependent apparent slip on hydrophobic surfaces: The Mattress Model
Recent experiments (Zhu & Granick (2001) Phys. Rev. Lett. 87 096105) have
measured a large shear dependent fluid slip at partially wetting fluid-solid
surfaces. We present a simple model for such slip, motivated by the recent
observations of nanobubbles on hydrophobic surfaces. The model considers the
dynamic response of bubbles to change in hydrodynamic pressure due to the
oscillation of a solid surface. Both the compression and diffusion of gas in
the bubbles decrease the force on the oscillating surface by a ``leaking
mattress'' effect, thereby creating an apparent shear-dependent slip. With
bubbles similar to those observed by atomic force microscopy to date, the model
is found to lead to force decreases consistent with the experimental
measurements of Zhu & Granick
Optimizing single-photon-source heralding efficiency at 1550 nm using periodically poled lithium niobate
We explore the feasibility of using high conversion-efficiency
periodically-poled crystals to produce photon pairs for photon-counting
detector calibrations at 1550 nm. The goal is the development of an appropriate
parametric down-conversion (PDC) source at telecom wavelengths meeting the
requirements of high-efficiency pair production and collection in single
spectral and spatial modes (single-mode fibers). We propose a protocol to
optimize the photon collection, noise levels and the uncertainty evaluation.
This study ties together the results of our efforts to model the single-mode
heralding efficiency of a two-photon PDC source and to estimate the heralding
uncertainty of such a source.Comment: 14 pages, 2 tables and 3 figures, final version accepted by
Metrologi
On the Aggregation of Inertial Particles in Random Flows
We describe a criterion for particles suspended in a randomly moving fluid to
aggregate. Aggregation occurs when the expectation value of a random variable
is negative. This random variable evolves under a stochastic differential
equation. We analyse this equation in detail in the limit where the correlation
time of the velocity field of the fluid is very short, such that the stochastic
differential equation is a Langevin equation.Comment: 16 pages, 2 figure
Home care needs of extremely obese elderly european women
Objective: To examine the health and needs of extremely obese women aged over 65 years receiving home care in Europe. Study design: A cross-sectional assessment study based on the Aged in Home Care (AdHOC) project recruited 2974 women aged 65 or over who were receiving home care at 11 sites in European countries. Extreme obesity was defined as ‘Obesity of such a degree as to interfere with normal activities, including respiration’.
Main outcome measures: Resident Assessment Instrument for Home Care (RAI-HC version 2.0); Activity of Daily Living Scale; Instrumental Activity of Daily Living Scale; the Minimum Data Set Cognitive Performance Scale; and a health profile.
Results: One hundred and twenty women (4.0%) were extremely obese. They were younger than their thinner counterparts, with a median age of 78.3 versus 83.3 years, and they more often had multiple health complaints and needed more help with mobility outside the home. The extremely obese had received home care longer than the non-extremely obese (median 28.7 versus 36.6 months). Extremely obese women also needed more help with personal care than the other group and, due to lower age, they were less cognitively impaired.
Conclusions: Extreme obesity is a problem that increasingly affects home care of elderly women
Semisimplicity of the quantum cohomology for smooth Fano toric varieties associated with facet symmetric polytopes
The degree zero part of the quantum cohomology algebra of a smooth Fano toric
symplectic manifold is determined by the superpotential function, W, of its
moment polytope. In particular, this algebra is semisimple, i.e. splits as a
product of fields, if and only if all the critical points of W are
non-degenerate. In this paper we prove that this non-degeneracy holds for all
smooth Fano toric varieties with facet-symmetric duals to moment polytopes.Comment: 16 pages; corrected version, published in Electron. Res. Announc.
Math. Sc
UV-induced ligand exchange in MHC class I protein crystals
High-throughput structure determination of protein−ligand complexes is central in drug development and structural proteomics. To facilitate such high-throughput structure determination we designed an induced replacement strategy. Crystals of a protein complex bound to a photosensitive ligand are exposed to UV light, inducing the departure of the bound ligand, allowing a new ligand to soak in. We exemplify the approach for a class of protein complexes that is especially recalcitrant to high-throughput strategies: the MHC class I proteins. We developed a UV-sensitive, “conditional”, peptide ligand whose UV-induced cleavage in the crystals leads to the exchange of the low-affinity lytic fragments for full-length peptides introduced in the crystallant solution. This “in crystallo” exchange is monitored by the loss of seleno-methionine anomalous diffraction signal of the conditional peptide compared to the signal of labeled MHC β2m subunit. This method has the potential to facilitate high-throughput crystallography in various protein families
LiQD Cornea: Pro-regeneration collagen mimetics as patches and alternatives to corneal transplantation
Transplantation with donor corneas is the mainstay for treating corneal blindness, but a severe worldwide shortage necessitates the development of other treatment options. Corneal perforation from infection or inflammation is sealed with cyanoacrylate glue. However, the resulting cytotoxicity requires transplantation. LiQD Cornea is an alternative to conventional corneal transplantation and sealants. It is a cell-free, liquid hydrogel matrix for corneal regeneration, comprising short collagen-like peptides conjugated with polyethylene glycol and mixed with fibrinogen to promote adhesion within tissue defects. Gelation occurs spontaneously at body temperature within 5 min. Light exposure is not required-particularly advantageous because patients with corneal inflammation are typically photophobic. The self-assembling, fully defined, synthetic collagen analog is much less costly than human recombinant collagen and reduces the risk of immune rejection associated with xenogeneic materials. In situ gelation potentially allows for clinical application in outpatient clinics instead of operating theaters, maximizing practicality, and minimizing health care costs
A high-brightness source of polarization-entangled photons optimized for applications in free space
We present a simple but highly efficient source of polarization-entangled
photons based on spontaneous parametric down-conversion (SPDC) in bulk
periodically poled potassium titanyl phosphate crystals (PPKTP) pumped by a 405
nm laser diode. Utilizing one of the highest available nonlinear coefficients
in a non-degenerate, collinear type-0 phase-matching configuration, we generate
polarization entanglement via the crossed-crystal scheme and detect 0.64
million photon pair events/s/mW, while maintaining an overlap fidelity with the
ideal Bell state of 0.98 at a pump power of 0.025 mW
Class I major histocompatibility complexes loaded by a periodate trigger
Class I major histocompatibility complexes (MHCs) present peptide ligands on the cell surface for recognition by appropriate cytotoxic T cells. The unstable nature of unliganded MHC necessitates the production of recombinant class I complexes through in vitro refolding reactions in the presence of an added excess of peptides. This strategy is not amenable to high-throughput production of vast collections of class I complexes. To address this issue, we recently designed photocaged MHC ligands that can be cleaved by a UV light trigger in the MHC bound state under conditions that do not affect the integrity of the MHC structure. The results obtained with photocaged MHC ligands demonstrate that conditional MHC ligands can form a generally applicable concept for the creation of defined peptide−MHCs. However, the use of UV exposure to mediate ligand exchange is unsuited for a number of applications, due to the lack of UV penetration through cell culture systems and due to the transfer of heat upon UV irradiation, which can induce evaporation. To overcome these limitations, here, we provide proof-of-concept for the generation of defined peptide−MHCs by chemical trigger-induced ligand exchange. The crystal structure of the MHC with the novel chemosensitive ligand showcases that the ligand occupies the expected binding site, in a conformation where the hydroxyl groups should be reactive to periodate. We proceed to validate this technology by producing peptide−MHCs that can be used for T cell detection. The methodology that we describe here should allow loading of MHCs with defined peptides in cell culture devices, thereby permitting antigen-specific T cell expansion and purification for cell therapy. In addition, this technology will be useful to develop miniaturized assay systems for performing high-throughput screens for natural and unnatural MHC ligands
- …