Substitution mechanism of alkali metals for strontium in strontium hydroxyapatite

Strontium hydroxyapatites substituted by alkali metals are synthesized by double decomposition method in basic medium. Structures of Sr_9.50Na_0.30(PO₄)₆(OH)_1.30 (SrNaHAp) and Sr_9.81K_0.12(PO₄)₆(OH)_1.74 (SrKHAp) are determined by X-ray powder diffraction. Both compounds are isotypic and crystallize in hexagonal system (space group P63/m) with the following cells: a=9.751(3) Å and c=7.279(3) Å for SrNaHAp and a=9.755(4) Å and c=7.284(3) Å for SrKHAp. Results are compared to those of Sr₁₀(PO₄)₆(OH)₂. According to the site occupancy factors, in SrNaHAp sodium is localized in site (I) and in SrKHAp potassium in site (II). Both structures contain vacancies in hydroxyl and metal sites. The mechanism of alkali metals substitution for strontium proposed explains the vacancies formation.     

A deformable subreflector for the Haystack radio telescope

A deformable subreflector was designed and implemented to compensate for part of the gravity deformations of the primary reflector of Haystack, a 37-m-(120-ft-)diameter Cassegrain radio telescope. This was done to allow it to operate at 100+ GHz, as compared to the 1-to-10 GHz range for which it was originally designed. The design, analysis, construction, testing, and the results of preliminary measurements of performance are presented. The deformable subreflector consists of a fiberglass shell, supported on an aluminum back structure. The homologous components of deformations are compensated for by optimal positioning of the subreflector, which can be displaced axially and laterally, and tilted. The deformation modes of the subreflector compensate for astigmatic deformations of the back structure of the primary, and for part of the symmetric and anti-symmetric components of gravity sag of the panels of the primary reflector. Analyses show that, due to the deformable subreflector, the surface RMS due to gravity has been reduced from 494 mm (19.4 mil) down to 146 mm (5.7 mil), as the antenna travels over its operating range of 15 to 70 degrees elevation. Combining the reduced gravity effects with surface adjustment and thermal errors results in a predicted combined surface error of 250 mm (9.8 mil), at the extremes of the operating range.<>     

Prevalence of NIDDM and impaired glucose tolerance in a rural and an urban population in Cameroon

PURPOSE: We wished to determine the effects of seizure type, age at onset, and family history of epilepsy on risk of spontaneous abortion in the pregnancies of adults with idiopathic/cryptogenic epilepsy. METHODS: We examined pregnancy outcomes in 812 adults with idiopathic/cryptogenic epilepsy who had ever had or fathered a pregnancy and 250 of their same sex siblings who had ever had or fathered a pregnancy. We compared the likelihood of spontaneous abortion before and after onset of epilepsy with the likelihood of spontaneous abortion among same sex siblings. RESULTS: Risk of spontaneous abortion was not increased before onset of epilepsy. After onset of epilepsy, risk of spontaneous abortion was significantly increased in the pregnancies of wives of men who had localization-related epilepsy with age at onset <10 years or who did not have a family history of epilepsy. In women after onset of epilepsy, risk of spontaneous abortion was significantly increased for pregnancies of women with localization-related epilepsy with age at onset < or =20 years and for those of women with or without a family history of epilepsy. Risk of spontaneous abortion was greatest in the pregnancies of women with a positive family history of epilepsy odds ratio, (OR = 2.12, p < 0.05). CONCLUSIONS: Risk of spontaneous abortion in the pregnancies of men and women with idiopathic/cryptogenic epilepsy varied with the clinical characteristics of their epilepsy. The increased risk of spontaneous abortion in women with a family history of epilepsy may influence the observed risk of epilepsy in their live-born offspring.     

Online decentralized information gathering with spatial–temporal constraints

We are interested in coordinating a team of autonomous mobile sensor agents in performing a cooperative information gathering task while satisfying mission-critical spatial–temporal constraints. In particular, we present a novel set of constraint formulations that address inter-agent collisions, collisions with static obstacles, network connectivity maintenance, and temporal-coverage in a resource-efficient manner. These constraints are considered in the context of the target search problem, where the team plans trajectories that maximize the probability of target detection. We model constraints continuously along the agents’ trajectories and integrate these constraint models into decentralized team planning using a computationally efficient solution method based on the Lagrangian formulation and decentralized optimization. We validate our approach in simulation with five UAVs performing search, and through hardware experiments with four indoor mobile robots. Our results demonstrate team planning with spatial–temporal constraints that preserves the performance of unconstrained information gathering and is feasible to implement with reasonable computational and communication resources.     

Network protection codes: Providing self-healing in autonomic networks using network coding

Agile recovery from link failures in autonomic communication networks is essential to increase robustness, accessibility, and reliability of data transmission. However, this must be done with the least amount of protection resources, while using simple management plane functionalities. Recently, network coding has been proposed as a solution to provide agile and cost efficient self-healing against link failures, in a manner that does not require data rerouting, packet retransmission, or failure localization, hence leading to simple control and management planes. To achieve this, separate paths have to be provisioned to carry encoded packets, hence requiring either the addition of extra links, or reserving some of the resources for this purpose.In this paper we introduce self-healing strategies for autonomic networks in order to protect against link failures. The strategies are based on network coding and reduced capacity, which is a technique that we call network protection codes (NPC). In these strategies, an autonomic network is able to provide self-healing from various network failures affecting network operation. Also, network protection codes are extended to provide self-healing from multiple link failures in autonomic networks. Although this leads to reducing the network capacity, the network capacity reduction is asymptotically small in most cases of practical interest. We provide implementation aspects of the proposed strategies, derive bounds and show how to construct network protection code. The paper also develops an Integer Linear Program formulation to evaluate the cost of provisioning connections using the proposed strategies, and uses results from this formulation to show that it is more resource efficient than 1 + 1 protection. A simulation study to evaluate the recovery times, and the buffering requirements due to network coding is also conducted using the OPNET simulator.     

Change detection in urban areas from remote sensing data: a multidimensional classification scheme

Change detection (CD) from remote sensing data is a very challenging research problem, especially when we analyse an urban scene. Urban scenes are composed of many different types of objects, both natural and man-made. The building class is one of the important and most complex classes to analyse, important because it is useful for so many applications and complex because it exhibits many changes due to human activity and natural catastrophes. For these reasons, we focus our study on building change detection (BCD). In this paper we propose a classification scheme for BCD research according to several important dimensions including objective, input data, temporal resolution, analysis unit, target output unit, building features, processing technique, change categories, and assessment of results. This classification scheme can guide practitioners in choosing appropriate change detection methods to achieve their goals as well as informing new research efforts. Based on this multidimensional characterisation of BCD, we offer a number of suggestions for further work to be done in this field.     

利用神经网络控制连续浇铸过程中的热传导

In continuous casting, the cooling-solidification process must be based on the adaptation of heat transfer, which is directly connected to casting conditions such as casting speed, casting temperature, and cooling parameters. Most control schemes are based on the static relation between casting speed and water flow rate in each cooling zone; this constitutes an open loop that does not consider the dynamic surface temperature, which is an important parameter for the final slab quality. In steelmaking, the casting-speed changes affect the global heat transfer. An optimal operation requires an adjustment of the process control variables, i.e., global heat transfer. A learning neural network (NN) allows the identification and the control of a nonlinear heat transfer model in the continuous casting process. A heat transfer model was developed using the dynamic heat balance. A comparison between the experimental open loop results and those of the model simulation is considered. Following adaptation, the model is used for controlling the slab surface temperature in closed loop, using NN technology and PID controllers. The NN identification and control strategy gives a stable temperature closed loop control comparatively to the conventional PID.     

On the accuracy of two analytical models for evaluating the performance of Gigabit Ethernet hosts

In this paper we develop and assess the accuracy of two analytical models that capture the behavior of network hosts when subjected to heavy load such as that of Gigabit Ethernet. The first analytical model is based on Markov processes and queuing theory, and the second is a pure Markov process. In order to validate the models and assess their accuracy, two different numerical examples are presented. The two numerical examples use system parameters that are realistic and appropriate for modern hardware. Both analytical models give closed-form solutions that facilitate the study of a number of important system performance metrics. These metrics include throughput, latency, stability condition, CPU utilizations of interrupt handling and protocol processing, and CPU availability for user applications. The two models give mathematically equivalent closed-form solutions for all metrics except for latency. To address latency, we compare the results of both models with the results of a discrete-event simulation. The latency accuracy of the two models is assessed relative to simulation in terms of differences and percentage errors. The paper shows that the second model is more accurate.     

Use of thermally stimulated discharge current for the study of rotational mobility of 4-mercaptoacetamidodiphenylamine in poly(vinyl chloride)

Thermally stimulated depolarization current (TSDC) of PVC containing 4-mercaptoacetamidodiphenylamine was studied. The current peak height (α-relaxation peak), maximum temperature, and activation energies were found to be influenced by the additive. The results suggest that no internal plasticization occurs in the system. The α-relaxation broadening was found to originate from a distribution of activation energies according to the rotation of the amide group of the additive.