Analytical modeling of bidirectional multi‐channel IEEE 802.11 MAC protocols

This paper presents an analytical approach to model the bi‐directional multi‐channel IEEE 802.11 MAC protocols (Bi‐MCMAC) for ad hoc networks. Extensive simulation work has been done for the performance evaluation of IEEE 802.11 MAC protocols. Since simulation has several limitations, this work is primarily based on the analytical approach. The objective of this paper is to show analytically the performance advantages of Bi‐MCMAC protocol over the classical IEEE 802.11 MAC protocol. The distributed coordination function (DCF) mode of medium access control (MAC) is considered in the modeling. Two different channel scheduling strategies, namely, random channel selection and fastest channel first selection strategy are also presented in the presence of multiple channels with different transmission rates. M/G/1 queue is used to model the protocols, and stochastic reward nets (SRNs) are employed as a modeling technique as it readily captures the synchronization between events in the DCF mode of access. The average system throughput, mean delay, and server utilization of each MAC protocol are evaluated using the SRN formalism. We also validate our analytical model by comparison with simulation results. The results obtained through the analytical modeling approach illustrate the performance advantages of Bi‐MCMAC protocols with the fastest channel first scheduling strategy over the classical IEEE 802.11 protocol for TCP traffic in wireless ad hoc networks. Copyright © 2010 John Wiley & Sons, Ltd.     

Monte Carlo-aided dosimetry of a new high dose-rate brachytherapy source

In this article we introduce a new high-intensity 192Ir source design for use in a recently reengineered microSelectron-HDR remote afterloading device for high dose-rate (HDR) brachytherapy. The maximum rigid length and outer diameter of the new source are reduced to 4.95 and 0.90 mm, respectively, compared to 5.50 and 1.10 mm for the previous source design introduced in 1991. In addition, a smaller diameter and more flexible steel cable are used, allowing the source cable to negotiate smaller diameter catheters or more tortuously curved catheters. Using Monte Carlo photon transport simulation, the complete two-dimensional (2-D) dose-rate distribution is calculated over the 0.1-7 cm distance range and are presented both as conventional 2-D Cartesian lookup tables and in the formalism recommended by the American Association of Physicists in Medicine Task Group 43 (TG-43) Report. The dose distribution of this source is very similar to that of its predecessor, except near the source tip and in the shadow of the cable assembly, where differences of 5%-8% are apparent. The accuracy of various methods for extrapolating beyond the tubulated anisotropy functions to short distances is evaluated. It is demonstrated that linear extrapolation from the anisotropy functions defined by TG-43 accurately (+/- 2%) estimates dose rate at short and long distances lying outside the radial distance range of the original measured data from which the anisotropy and radial dose functions were derived. In contrast, the algorithm used on the vendor's planning system results in large calculation errors at distances less than 5 mm.     

Virally inactivated fresh frozen plasma

Several technologies are now available to treat whole fresh-frozen plasma (FFP) to inactivate transfusion-transmitted viruses, including pasteurisation, solvent/detergent and methylene blue/light. The first two involve creating large plasma pools prior to inactivation, while only pasteurisation clearly destroys both enveloped and non-enveloped viruses. Some of the issues surrounding the use of these products include demonstration of both clinical efficacy and improved viral safety, and the need for product licencing. Potential benefits must be balanced against the risks of plasma pooling, while the increased costs will require comparison with other strategies such as quarantining of plasma. It is also recognised that reducing inappropriate FFP usage will play a role in improved patient safety.     

Closely spaced recurrent hippocampal seizures elicit two types of heightened epileptogenesis: a rapidly developing, transient kindling and a slowly developing, enduring kindling

Kindling is widely accepted as a model of chronic epilepsy as well as a model of plasticity in the nervous system. Conventional kindling studies have used infrequent stimuli (separated by many hours) to establish a fully kindled state in which enhanced responses (kindled motor seizures and protracted afterdischarges) are consistently triggered by stimuli that initially did not elicit such responses. The enhanced responses occur even after a prolonged stimulus-free interval. Whereas the establishment of a kindled state with traditional stimulus protocols takes several weeks, our previous work showed that kindling could take place much more quickly when the interstimulus interval was set at 30 min (rapid kindling). In this report we tested whether rapid kindling protocols share with traditional kindling protocols the ability to establish a fully kindled state. Using different stimulus protocols involving recurrent hippocampal seizures, we characterized two types of kindling. 'Rapid kindling' developed over hours, but was transient, with a decay rate of a few days so that a fully kindled state did not persist. In contrast, 'slow kindling' developed over several weeks and was enduring, apparently permanent, being associated with a fully kindled state. These findings suggest that, while having certain similarities, the two types of kindling arise from dissimilar mechanisms. The existence of these two types of kindling has implications for epileptogenesis in humans. Moreover, the protocols developed in this work provide a useful means to control for the effects of seizures that are not related to mechanisms underlying a fully kindled state.     

Effects of age, breast density, ethnicity, and estrogen replacement therapy on screening mammographic sensitivity and cancer stage at diagnosis: review of 183,134 screening mammograms in Albuquerque, New Mexico

PURPOSE: To examine how common patient factors affect screening mammographic sensitivity and cancer stage at diagnosis. MATERIALS AND METHODS: The authors used a population-based database of 183,134 screening mammograms and a statewide tumor registry to identify 807 breast cancers detected at screening mammography. RESULTS: Sensitivity varied significantly with ethnicity, use of estrogen replacement therapy, mammographic breast density, and age. Sensitivity was 54% (13 of 24) in women younger than 40 years, 77% (121 of 157) in women aged 40-49 years, 78% (224 of 286) in women aged 50-64 years, and 81% (277 of 340) in women older than 64 years. Sensitivity was 68% (162 of 237) for dense breasts and 85% (302 of 356) for nondense breasts and 74% (180 of 244) in estrogen replacement therapy users and 81% (417 of 513) in nonusers. Sensitivity was most markedly reduced with the combination of dense breasts and estrogen replacement therapy use; there was little difference when only one factor was present. Median cancer size and the percentage of early cancers showed little change with any factors. CONCLUSION: Age is a minor determinant of mammographic sensitivity in women aged 40 years or older. Sensitivity is substantially decreased with the combination of higher breast density and estrogen replacement therapy use. There was not a notable shift in cancer outcomes in the groups with lower mammographic sensitivity. These data do not support different screening recommendations in women aged 40-49 years or in estrogen replacement therapy users.     

Prophylactic gene therapy for cancer

BACKGROUND: Epithelial ovarian tumors of borderline malignancy are different from benign tumors and malignant neoplasms. They exist with relatively benign clinical course, younger age and better prognosis as compared with invasive malignant carcinomas. Most of them are discovered at early stage, for example, stage Ia. This retrospective review evaluates the clinical features, treatments and prognosis of 48 patients with borderline malignancy of ovarian tumors. METHODS: Forty-eight patients with ovarian tumors of borderline malignancy, aged from 14 to 69 years (mean: 39.2 years; median: 36 years), were retrospectively studied. The histopathologic diagnosis was based on the morphologic criteria published by Tazelaar et al. in 1985. All cases, including 16 cases diagnosed before 1985, were pathologically reviewed. All information of clinical stage, surgical intervention and prognosis was achieved by reviewing hospital record or contacting patients by telephone. Two patients were lost to follow up. One patient died of sepsis resulting from another operation for another gynecological cancer. Totally forty-five patients were included for evaluation. RESULTS: Thirty-nine of the 48 patients (81.3%) were at stage Ia, 6 cases (12.5%) were at stage Ib, 2 cases (4.1%) were at stage Ic, and the remaining one patient (2.1%) was at state IIIc. Thirty-four patients (71%) were with mucinous cystadenoma of borderline malignancy, 11 cases (23%) were of serous type, and 3 patients (6%) were of mixed serous and mucinous type. Twenty-two patients underwent total abdominal hysterectomy and bilateral salpingo-oophorectomy (TAH and BSO), but one of them remained partial ovary due to young age (27 y/o). Twelve patients were treated with unilateral oophorectomy or unilateral salpingo-oophorectomy (USO). Twelve patients underwent USO and wedge resection of contralateral ovary. One case underwent debulking surgery. One patient underwent enucleation of ovarian tumor and biopsy of contralateral ovary. Eighteen patients were treated with chemotherapy after operation. One patient developed recurrence 4 months after the primary operation. Excluding two cases lost to follow up and one case with surgical mortality for another gynecological cancer, forty-five patients were alive and were followed from 9 months to 165 months. (median: 48 months; mean: 46 months) CONCLUSIONS: Most of the patients were at the early stage of disease when first diagnosed, 81.3% were at stage Ia and only one case was at stage IIIc. Sixty-three percent of our patients underwent surgical treatment alone while the rest of them (37%) had post-operative chemotherapy with either alkeran or PAC. The use of adjuvant chemotherapy seemed unwarranted as there was no difference in survival between those with and without it. (P > 0.05) The low recurrent rate of 2% in our patients again confirmed the 9 P relative benign clinical course of this disease.     

Small-angle neutron scattering studies of hot-wire CVD a-Si:H

Several a-Si:H and a-Si:D films prepared by hot-wire chemical vapor deposition have been examined by small-angle neutron scattering (SANS) to search for H non-uniformity in this material. The SANS measurements were supplemented by small-angle X-ray scattering measurements. The differences in H/D detection sensitivity of these two techniques allow distinction of the scattering mechanisms. Two- or three-phase models are used to interpret the results quantitatively. Significant H non-uniformity, as well as a small fraction of microvoids, was found in the best-quality material. Samples grown with higher deposition rates or lower substrate temperatures have much larger void fractions. The size scale of the heterogeneity spans a range from 2 nm to more than 50 nm, with the largest features assigned to surface roughness.     

Ultrafast long-wavelength photodetectors fabricated onlow-temperature InGaAs on GaAs

The authors report the first successful demonstration of a metal-semiconductor-metal photodetector (MSMPD) fabricated on low-temperature InGaAs grown on GaAs by molecular beam epitaxy (MBE) for long-wavelength fiber optic applications. Interdigitated MSMPDs with finger widths and spacings of 0.2, 0.5, 1.0, and 2.0 μm were tested using a femtosecond pulsed laser and high-speed electrooptic sampling. A FWHM pulsed response of 2 and 1.3 ps was measured for low-temperature In _0.25Ga_0.75As and In_0.35Ga_0.65As, respectively. The latter is the fastest response reported to data for a photodetector capable of detection to wavelengths as long as 1.3 μm