A Transmissive X-ray Polarimeter Design For Hard X-ray Focusing Telescopes

The X-ray Timing and Polarization (XTP) is a mission concept for a future space borne X-ray observatory and is currently selected for early phase study. We present a new design of X-ray polarimeter based on the time projection gas chamber. The polarimeter, placed above the focal plane, has an additional rear window that allows hard X-rays to penetrate (a transmission of nearly 80% at 6 keV) through it and reach the detector on the focal plane. Such a design is to compensate the low detection efficiency of gas detectors, at a low cost of sensitivity, and can maximize the science return of multilayer hard X-ray telescopes without the risk of moving focal plane instruments. The sensitivity in terms of minimum detectable polarization, based on current instrument configuration, is expected to be 3% for a 1mCrab source given an observing time of 10^5 s. We present preliminary test results, including photoelectron tracks and modulation curves, using a test chamber and polarized X-ray sources in the lab

Restoration of Corneal Stiffness in Rabbits Following Withdrawal of Travoprost.

PurposeTo evaluate if the effect of travoprost on corneal material stiffness could be restored after drug withdrawal.MethodsSeventy-two rabbits were randomly allocated into three groups: medicine (M), medicine withdrawal (MW), and blank (B). Within the M and MW groups, treatment with travoprost was administered to the right eyes (MT and MWT) over a period of 12 weeks. Subsequently, the M group was killed, but the MW group underwent an additional 12-week period for treatment withdrawal. No treatment was given to the contralateral eyes (MC and MWC) in the M and MW groups. A separate blank control (BC) group remained untreated for the entire 24-week duration. In each group, corneas from 18 rabbits were tested mechanically under inflation conditions to estimate their tangent modulus (Et). The corneas of the remaining six rabbits underwent electron microscopy analysis, which focused on fibril diameter and interfibrillar spacing.ResultsCentral corneal thickness (CCT) of the treated eyes (MT and MWT groups) decreased with 12 weeks of travoprost treatment (P 0.05).ConclusionsTravoprost treatment appears to soften corneal tissue, decrease tissue thickness, and reduce the density of stromal collagen fibers by increasing the interfibrillar spacing. These changes were partially reversed after treatment cessation. Travoprost could further inhibit corneal growth, so its use in childhood and adolescence should be carefully considered. Additionally, the effect of travoprost in reducing corneal stiffness may lead to underestimations of intraocular pressure (IOP) measurement and hence overestimations in the effect of treatment in lowering IOP

Droplet spreading, substrate remelting and variable thermal contact resistance in microcasting

A profound understanding of the molten droplet solidification and substrate remelting process in microcasting is necessary to optimize the operation parameters, such as impact velocity, droplet superheat and substrate temperature, thereby to produce good quality products.A numerical model considering the complex fluid dynamics of droplet spreading, the flow of substrate melt, and the thermal contact resistance between the droplet and the substrate was introduced. The results of numerical simulation were compared with a previous microcasting experiment. It has been found that the fluid dynamics and heat transfer are strongly coupled so that the thermal contact resistance can not only affect the droplet spreading but also the profiles of maximum substrate remelting front. The effects of operation parameters on rnicrocasting were also described in detail.The variable thermal contact resistance between the solidifying alloy158 and the substrate of the same material was investigated experimentally. A novel inverse heat transfer method based on the measurement of ultrasonic time delay was developed to estimate the variable thermal contact resistance. It has been found that the variation of thermal contact resistance to a large degree determined by the contact interface temperatures. The influences of the initial molten metal temperature and the impact velocity on the formation of thermal contact resistance were investigated. An empirical correlation equation of variable thermal contact resistance, which can be applied to the numerical simulation of molten droplet impact, was developed utilizing the experimental data.The experimental investigation of the impact of highly superheated molten alloy158 droplets onto alloy158 substrates was conducted. The detailed droplet spreading and recoiling process was captured using a high speed CCD camera. The effects of the impact velocity and the molten droplet temperature were investigated in detail. It has been found that whether the droplet spreading can be arrested by the solidification at the edge of droplet during the spreading or the recoiling period depends on the droplet temperature and the impact velocity.The numerical simulation with the application of variable thermal contact resistance was conducted to compare with experimental results. It has demonstrated that the numerical simulations can predict the droplet spreading and recoiling process correctly, verifying the feasibility of using a variable thermal contact resistance in the numerical simulation of the molten droplet impact, and making the numerical simulations more powerful in prediction.</p