Initial Window Research Articles

Comparative Outcomes of Tenofovir-Based and Zidovudine-Based Antiretroviral Therapy Regimens in Lusaka, Zambia

Although tenofovir (TDF) is a common component of antiretroviral therapy (ART), recent evidence suggests inferior outcomes when it is combined with nevirapine (NVP). We compared outcomes among patients initiating TDF + emtricitabine or lamivudine (XTC) + NVP, TDF + XTC + efavirenz (EFV), zidovudine (ZDV) + lamuvidine (3TC) + NVP, and ZDV + 3TC + EFV. We categorized drug exposure by initial ART dispensation by a time-varying analysis that accounted for drug substitutions and by predominant exposure (>75% of drug dispensations) during an initial window period. Risks for death and program failure were estimated using Cox proportional hazard models. All regimens were compared with ZDV + 3TC + NVP. Between July 2007 and November 2010, 18,866 treatment-naive adults initiated ART: 18.2% on ZDV + 3TC + NVP, 1.8% on ZDV + 3TC + EFV, 36.2% on TDF + XTC + NVP, and 43.8% on TDF + XTC + EFV. When exposure was categorized by initial prescription, patients on TDF + XTC + NVP [adjusted hazard ratio (AHR): 1.45; 95% confidence interval (CI): 1.03 to 2.06] had a higher post-90-day mortality. TDF + XTC + NVP was also associated with an elevated risk for mortality when exposure was categorized as time-varying (AHR: 1.51; 95% CI: 1.18 to 1.95) or by predominant exposure over the first 90 days (AHR: 1.91, 95% CI: 1.09 to 3.34). However, these findings were not consistently observed across sensitivity analyses or when program failure was used as a secondary outcome. TDF + XTC + NVP was associated with higher mortality when compared with ZDV + 3TC + NVP but not consistently across sensitivity analyses. These findings may be explained in part by inherent limitations to our retrospective approach, including residual confounding. Further research is urgently needed to compare the effectiveness of ART regimens in use in resource-constrained settings.

Information and Prediction Criteria in Selecting the Forecasting Model

The purpose of the paper it to compare the performance of both information and prediction criteria in selecting the forecasting model on empirical data for Poland when the data generating model is unknown. The attention will especially focus on the evolution of information criteria (AIC, BIC) and accumulated prediction error (APE) for increasing sample sizes and rolling windows of different size, and also the impact of initial sample and rolling window sizes on the selection of forecasting model. The best forecasting model will be chosen from the set including three models: autoregressive model, AR (with or without a deterministic trend), ARIMA model and random walk (RW) model.

Heart rate as an independent risk factor in patients with multiple organ dysfunction: a prospective, observational study

To study the association between baseline heart rate and outcome in patients with multiple organ dysfunction (MODS) as well as the course of heart rate over the first 4days during MODS. Prospective observational study in 89 patients with MODS, defined as an APACHE-II score ≥20. Baseline heart rate (HR(0)) was determined over a 60-minute period at the time of MODS diagnosis. 28-day all-cause mortality was the primary endpoint of the study, a fall of the APACHE-II score by 4 points or more from day 0 to day 4 constituted the secondary endpoint. Hazard ratios for heart rate of 90 beats per minute (bpm) or greater relative to less than 90bpm were calculated using Cox proportional hazards model and adjusted for confounding variables. Median baseline heart rate was 83bpm in survivors and 92bpm in non-survivors (p=0.048). 28-day mortality was 32 and 61% in patients with HR(0)<90bpm and HR(0)≥90bpm, respectively. The adjusted hazard ratio for 28-day mortality was 2.30 (95% confidence interval 1.21-4.36, p=0.001) for HR(0)≥90bpm relative to HR(0)<90bpm. No correlation was found between baseline heart rate and the secondary endpoint. From day 0 to day 4, heart rate remained elevated in all patients, as well as in survivors and non-survivors. A heart rate ≥90bpm at the time of MODS diagnosis is an independent risk factor for increased 28-day mortality. As in patients with cardiovascular conditions such as coronary heart disease or chronic heart failure, heart rate might constitute a target for heart rate-lowering therapy in the narrow initial treatment window of MODS.

Size-Dependent Trapping Effect in Nano-Dot Non-Volatile Memory

We report a flash memory using deep traps nano-dot formed in ZrON charge trapping layers by As+ implantation to improve the device performance of MONOS CTF device. The TaN-[SiO2-LaAlO3]-[As+-implanted ZrON]-[LaAlO3-SiO2]-Si device shows a 6 nm ENT, a large initial memory window of 9.8 V, a 10-year extrapolated retention window of 3.6 V at 85oC, and an endurance window of 5.1 V after 105 cycles under fast 100 μs and low μ16 V program/erase. The performance of As+-implanted ZrON is significantly better than that of stacked Si3N4/Ir-dot/HfON device with poor thickness scaling due to excess Ir metal dot.

Improved speed and data retention characteristics in flash memory using a stacked HfO2/Ta2O5 charge-trapping layer

This paper reports the simultaneous improvements in erase speed and data retention characteristics in flash memory using a stacked HfO2/Ta2O5 charge-trapping layer. In comparison to a memory capacitor with a single HfO2 trapping layer, the erase speed of a memory capacitor with a stacked HfO2/Ta2O5 charge-trapping layer is 100 times faster and its memory window is enlarged from 2.7 to 4.8 V for the same ±16 V sweeping voltage range. With the same initial window of ΔVFB = 4 V, the device with a stacked HfO2/Ta2O5 charge-trapping layer has a 3.5 V extrapolated 10-year retention window, while the control device with a single HfO2 trapping layer has only 2.5 V for the extrapolated 10-year window. The present results demonstrate that the device with the stacked HfO2/Ta2O5 charge-trapping layer has a strong potential for future high-performance nonvolatile memory application.

Power-saving mechanism with delay bound for Mobile WiMAX systems

In Mobile World Interoperability for Microwave Access (WiMAX), the power-saving mechanism (PSM), which operates alternately in sleep and awake modes, works to extend the lifetime of mobile stations (MSs), although it concurrently induces a medium access control (MAC) service data unit (SDU) response delay. In this study, the authors derive the analytical models for two of the most important performance metrics: the average power consumption and the average MAC SDU response delay of an MS in sleep mode. These metrics are given as a function of the sleep mode system parameters: initial sleep window Tmin and final sleep window Tmax. Based on these models, the authors show that a tradeoff relationship exists between them. The authors then propose an optimised power-saving mechanism (OPSM) that jointly determines the optimal Tmin and Tmax to minimise the power consumption under a given MAC SDU response delay constraint. Through both numerical analyses and subsequent simulations, the authors show that the OPSM effectively minimises the power consumption of an MS in its sleep mode while guaranteeing the MAC SDU response delay constraint.

Auxin minimum defines a developmental window for lateral root initiation

Root system architecture depends on lateral root (LR) initiation that takes place in a relatively narrow developmental window (DW). Here, we analyzed the role of auxin gradients established along the parent root in defining this DW for LR initiation. Correlations between auxin distribution and response, and spatiotemporal control of LR initiation were analyzed in Arabidopsis thaliana and tomato (Solanum lycopersicum). In both Arabidopsis and tomato roots, a well defined zone, where auxin content and response are minimal, demarcates the position of a DW for founder cell specification and LR initiation. We show that in the zone of auxin minimum pericycle cells have highest probability to become founder cells and that auxin perception via the TIR1/AFB pathway, and polar auxin transport, are essential for the establishment of this zone. Altogether, this study reveals that the same morphogen-like molecule, auxin, can act simultaneously as a morphogenetic trigger of LR founder cell identity and as a gradient-dependent signal defining positioning of the founder cell specification. This auxin minimum zone might represent an important control mechanism ensuring the LR initiation steadiness and the acropetal LR initiation pattern.

A new analytical model for the IEEE 802.15.4 CSMA-CA protocol

We give new analytical results for the performance of a wireless sensor network using the energy-conserving CSMA-CA MAC protocol of IEEE 802.15.4. We derive the throughput both under saturation and under a nonsaturation scenario in a star network involving periodic traffic, and validate the accuracy of our results using simulation for both acknowledgement and non-acknowledgement modes. Our analysis relies on the solution of a fixed point equation, and we prove the existence and uniqueness of the fixed point for the saturated case. The initial backoff window that maximizes saturation throughput is derived, and shown to be an approximately linear function of the number of active nodes. We also study the saturation model when the number of nodes tends to infinity, and obtain a simple expression for the asymptotic throughput.

Do Wealth Creating Mergers and Acquisitions Really Hurt Acquirer Shareholders?

We examine the expected economic benefits of mergers and acquisitions. We conclude that both signaling and revelation biases are responsible for the commonly reported finding that on average takeovers are harmful to acquirer shareholder wealth. After accounting for these two biases that lead to a price fall on announcement of 18.9% ($563.9 million), we demonstrate that acquirers generally benefit from takeovers with an average 81% share of the economic gains from the transaction. By studying bids that fail for exogenous reasons, which are largely free of signaling and revelation biases, we confirm the neoclassical view that takeovers are positive NPV projects for a typical acquirer, which produce a sizeable return on capital of 21% to the acquirer ($626.6 million) and 21.2% ($772.2 million) to the combined acquirer-target. This conclusion is based on two important findings. First, on a failed acquisition announcement, the combined acquirer and target value on average falls, where both target and acquirer suffer significant negative abnormal returns. Second, acquirers share in a significant portion of the economic benefits of a successful acquisition, reflected in a significantly positive relationship between acquirer and target stock returns utilizing a 60-day initial bid announcement window and a 100-day period following the termination announcement. Over the same window, exogenously failed cash bidders significantly underperform successful cash bidders by 10.7% and exogenously failed stock bidders significantly underperform successful stock bidders by a further 15.5% making a total differential of 26.2%. Moreover, in the long term, stock-funded targets typically only receive half the premium of cash targets.

Improved characteristics for Pd nanocrystal memory with stacked HfAlO–SiO 2 tunnel layer

Stacked HfAlO–SiO 2 tunnel layers are designed for Pd nanocrystal nonvolatile memories. For the sample with 1.5 nm-HfAlO/3.5 nm-SiO 2 tunnel layer, a smaller initial memory window is obtained compared to the sample with 3.5 nm-HfAlO/1.5 nm-SiO 2 tunnel layer. Owing to the thermally induced traps in HfAlO–SiO 2 films are located at a farther distance from the Si substrate and more effective blocking of charge leakage by asymmetric tunnel barrier, a larger final memory window and better retention characteristic can be obtained for Al/blocking oxide SiO 2/Pd NCs/1.5 nm-HfAlO/3.5 nm-SiO 2/Si structure. A N 2 plasma treatment can further improve the memory characteristics. Better memory characteristics can be obtained for Pd-nanocrystal-based nonvolatile memory with an adequate thickness ratio of HfAlO to SiO 2.

Measurement of CFA-Induced Hyperalgesia and Morphine-Induced Analgesia in Rats: Dorsal vs Plantar Mechanical Stimulation of the Hindpaw

To compare the sensitivity of stimulating the plantar and dorsal hindpaw surfaces in the detection of mechanical allodynia and morphine analgesia. Several approaches are used to assess nociceptive reactivity to mechanical stimulation in animal models of pain. Although certain techniques seem to be favored for studying specific nociceptive conditions, the differences between techniques have not been directly compared and characterized. We chose to compare methods employing stimulation applied to the dorsum of the paw with stimulation of the plantar surface to demonstrate the utility of each approach in determining baseline nociceptive thresholds, changes in those thresholds after injury, and analgesic efficacy. Withdrawal thresholds from mechanical stimulation applied to the dorsal and plantar surface of the hindpaw were measured in rats treated with morphine after receiving subcutaneous injections of complete Freund's adjuvant (CFA) using Semmes-Weinstein (S-W) monofilaments and electro von Frey (EVF) stimulation. In contrast to stimulation of the dorsal surface, plantar hindpaw stimulation seldom elicited an aversive withdrawal response. Differences in withdrawal response from baseline were only detectable within the first 5 hours post-CFA and only with EVF stimulation. No significant differences in stimulation techniques were observed after the initial 5-hour window. Effective dose 50 (ED(50)) for analgesic efficacy was consistently lower using dorsal stimulation. Stimulation of the plantar surface of the paw is superior for detecting small changes in paw sensitivity at very low stimulus intensities, whereas stimulation of the dorsal surface is superior for delineating baseline pain thresholds and for detecting robust analgesia. Reliable and sensitive assessment of animal pain behaviors is critical to translational pain research. This study demonstrates the importance of using proper test protocols in animal studies and its implication in preclinical screening of potential analgesics.

Arsenic-Implanted HfON Charge-Trapping Flash Memory With Large Memory Window and Good Retention

We have fabricated the TaN-[SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ]-HfON-[LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ]-Si charge-trapping Flash device. A large 6.4-V initial memory window, a 4.3-V 10-year extrapolated reten tion window at 125°C, and a 5.5-V endurance window at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> cycles were measured under very fast 100-μs and low ±16-V program/erase. These excellent results were achieved using an As <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> implant into the HfON trapping layer, which were sig nificantly better than those of the control device without ion implantation.

Analysis and enhancement of multi-channel MAC protocol for ad hoc networks

In this paper, an analytical model is proposed to calculate the network throughput of dedicated control channel protocols that are designed to schedule multiple packets to be transmitted on different data channels simultaneously. Based on the analytical model, a scheme by tuning the initial contention window size is proposed to maximize the network throughput. We also present a novel multi-channel MAC protocol for single-hop scenario. Simulation results show that the proposed model is capable of modeling the behaviors of dedicated control channel protocols accurately. Furthermore, the proposed scheme can reduce the cost of collisions and enhance the network throughput up to 22% for 1 kB packet size and 80 nodes. Compared with other dedicated control channel protocols, the proposed protocol can schedule more control packets and use multiple channels more efficiently. Copyright © 2010 John Wiley & Sons, Ltd. (An analytical model is proposed to calculate the network throughput of dedicated control channel protocols that are designed to schedule multiple packets to be transmitted on different data channels simultaneously. Based on the analytical model, a scheme by tuning the initial contention window size is proposed to maximize the network throughput. We also present a novel multi-channel MAC protocol for a single-hop scenario.)

Ovarian Hormone Deficiency Reduces Intrinsic Excitability and Abolishes Acute Estrogen Sensitivity in Hippocampal CA1 Pyramidal Neurons

Premature and uncompensated loss of ovarian hormones following ovariectomy (OVX) elevates the risks of cognitive impairment and dementia. These risks are prevented with estrogen (E(2))-containing hormone replacement therapy initiated shortly following OVX but not after substantial delay. Currently, the cellular bases underlying these clinical findings are unknown. At the cellular level, intrinsic membrane properties regulate the efficiency of synaptic inputs to initiate output action potentials (APs), thereby affecting neuronal communication, hence cognitive processing. This study tested the hypothesis that in CA1 pyramidal neurons, intrinsic membrane properties and their acute regulation by E(2) require ovarian hormones for maintenance. Whole-cell current-clamp recordings were performed on neurons from ∼ 7-month-old OVX rats that experienced either short-term (10 d, control OVX) or long-term (5 months, OVX(LT)) ovarian hormone deficiency. The results reveal that long-term hormone deficiency reduced intrinsic membrane excitability (IE) as measured by the number of evoked APs and firing duration for a given current injection. This was accompanied by AP broadening, an increased slow afterhyperpolarization (sAHP), and faster accumulation of Na(V) channel inactivation during repetitive firing. In the control OVX neurons, E(2) acutely increased IE and reduced the sAHP. In contrast, acute regulation of IE by E(2) was absent in the OVX(LT) neurons. Since the degree of IE of hippocampal pyramidal neurons is positively related with hippocampus-dependent learning ability, and modulation of IE is observed following successful learning, these findings provide a framework for understanding hormone deficiency-related cognitive impairment and the critical window for therapy initiation.

Comparison of end-to-end and network-supported fast startup congestion control schemes

A fundamental challenge for congestion control is the flow startup phase after the connection setup or after long idle periods. The Transmission Control Protocol (TCP) uses the time-consuming Slow-Start mechanism in that case. The objective of fast startup congestion control is to fully utilize a path much more rapidly. Faster startups can either be realized by new end-to-end congestion control mechanisms that change the Slow-Start algorithm, or by additional on-path signaling providing information about the path. This paper comprehensively compares end-to-end and network-supported fast startup schemes. We evaluate both the potential performance benefit and risk, using analytical models, simulation results, and experiments with real applications. Concerning end-to-end schemes, we study both a simple increase of the initial congestion window and the recently proposed Jump-Start mechanism. The considered network-supported schemes are the Quick-Start TCP extension and the Rate Control Protocol (RCP). They can all significantly reduce the transport delay of mid-sized data transfers, in particular over broadband networks with a non-negligible latency. As a result, fast startup schemes can significantly speed up Internet application with such traffic patterns. Our results also reveal that end-to-end approaches are not necessarily overly aggressive. Network-supported mechanisms can reduce the risk of congestion, but there are several unsolved open issues. In summary, we argue that end-to-end fast startup schemes such as an increased initial congestion window would be a promising solution for the Internet.

The performances study of IEEE 802.11e to support QoS in channel error environment

ABSTRACTOne of the most important functions in IEEE 802.11e is enhanced distributed coordination function (EDCF). EDCF is an enhanced version of IEEE 802.11 distributed coordination function (DCF) which provides a priority scheme by differentiating the inter‐frame space and the initial window size. We proposed a modified Markov chain model to study the EDCF priority scheme. We have theoretically analyzed the saturation throughput and delay by using the modified Markov chain model in non‐ideal channel scenario. We also have compared it with the Markov chain model that exists under ideal channel scenario. Simulations are also conducted to validate analytical results. Our study shows that the modified model under ideal channel scenario is better than that in channel error scenario. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Morphologically conditioned stress assignment in Choguita Rarámuri

This article investigates the morphologically conditioned stress system of a previously undocumented Uto-Aztecan language, Choguita Raramuri (Tarahumara). Stress distribution in Choguita Raramuri results from a complex interaction between lexically prespecified stress, two systematic subpatterns (second and third syllable stress), a stress rule specific to noun incorporation constructions, and an initial three-syllable window, a highly unusual typological pattern. This article presents a cophonology analysis that captures the full range of stress alternations in this language through the association of morphological constructions with fully general phonological subgrammars, and through the association of morphologically conditioned phonological effects to the hierarchical structure of morphologically complex words. The cophonology analysis is contrasted with a Root Controlled Accent (RCA) analysis, an indexed constraint analysis argued for in Alderete (2001a, 2001b) to account for the stress patterns of Cupeno, a Uto-Aztecan language with stress alternations similar to those attested in Choguita Raramuri. In an RCA analysis, stress alternations are derived through a single constraint ranking and faithfulness constraints indexed to specific morphological contexts. This article argues that an analysis that overlooks morphological constituency and which indexes faithfulness constraints to morphological environments undergenerates in the Choguita Raramuri case.

An adaptive SK technique and its application for fault detection of rolling element bearings

In this paper, we propose an adaptive spectral kurtosis (SK) technique for the fault detection of rolling element bearings. The primary contribution is adaptive determination of the bandwidth and center frequency. This is implemented with successive attempts to right-expand a given window along the frequency axis by merging it with its subsequent neighboring windows. Influence of the parameters such as the initial window function, bandwidth and window overlap on the merged windows as well as how to choose those parameters in practical applications are explored. Based on simulated experiments, it can be found that the proposed technique can further enhance the SK-based method as compared to the kurtogram approach. The effectiveness of the proposed method in fault detection of the rolling element bearings is validated using experimental signals.

An Energy and Application Scenario Aware Active RFID Protocol

The communication protocol used is a key issue in order to make the most of the advantages of active RFID technologies. In this paper we introduce a carrier sense medium access data communication protocol that dynamically adjusts its back-off algorithm to best suit the actual application at hand. Based on a simulation study of the effect on tag energy cost, read-out delay, and message throughput incurred by some typical back-off algorithms in a CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) active RFID protocol, we conclude that by dynamic tuning of the initial contention window size and back-off interval coefficient, tag energy consumption and read-out delay can be significantly lowered. We show that it is possible to decrease the energy consumption per tag payload delivery with more than 10 times, resulting in a 50% increase in tag battery lifetime. We also discuss the advantage of being able to predict the number of tags present at the RFID-reader as well as ways of doing it.

Highly scaled charge-trapping layer of ZrON nonvolatile memory device with good retention

We have fabricated the TaN–[SiO2–LaAlO3]–ZrON–[LaAlO3–SiO2]–Si charge-trapping flash device with highly scaled 3.6 nm equivalent-Si3N4-thickness. This device shows large 4.9 V initial memory window, and good retention of 3.4 V ten-year extrapolated retention window at 85 °C, under very fast 100 μs and low ±16 V program/erase. These excellent results were achieved using deep traps formed in ZrON trapping layer by As+ implantation that was significantly better than those of control device without ion implantation.