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Search Results: 1 - 10 of 401702 matches for " M. Lester "
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Observations of nightside auroral plasma upflows in the F-region and topside ionosphere
C. Foster,M. Lester
Annales Geophysicae (ANGEO) , 2003,
Abstract: Observations from the special UK EISCAT program UFIS are presented. UFIS is a joint UHF-VHF experiment, designed to make simultaneous measurements of enhanced vertical plasma flows in the F-region and topside ionospheres. Three distinct intervals of upward ion flow were observed. During the first event, upward ion fluxes in excess of 1013 m–2 s–1 were detected, with vertical ion velocities reaching 300 m s–1 at 800 km. The upflow was associated with the passage of an auroral arc through the radar field of view. In the F-region, an enhanced and sheared convection electric field on the leading edge of the arc resulted in heating of the ions, whilst at higher altitudes, above the precipitation region, strongly enhanced electron temperatures were observed; such features are commonly associated with the generation of plasma upflows. These observations demonstrate some of the acceleration mechanisms which can exist within the small-scale structure of an auroral arc. A later upflow event was associated with enhanced electron temperatures and only a moderate convection electric field, with no indication of significantly elevated ion tem- peratures. There was again some evidence of F-region particle precipitation at the time of the upflow, which exhibited vertical ion velocities of similar magnitude to the earlier upflow, suggesting that the behaviour of the electrons might be the dominant factor in this type of event. A third upflow was detected at altitudes above the observing range of the UHF radar, but which was evident in the VHF data from 600 km upwards. Smaller vertical velocities were observed in this event, which was apparently uncorrelated with any features observed at lower altitudes. Limitations imposed by the experimental conditions inhibit the interpretation of this event, although the upflow was again likely related to topside plasma heating.
Transfusion, erythropoiesis-stimulating agent therapy, and kidney transplant wait time  [PDF]
Robert M. Perkins, H. Lester Kirchner, Rajesh Govindasamy
Open Journal of Internal Medicine (OJIM) , 2012, DOI: 10.4236/ojim.2012.21001
Abstract: Aim: Anemia is highly prevalent among patients wait-listed for renal transplant, and management with blood transfusion or erythropoietin stimulating agents may impact transplant wait time. The purpose of this study was to examine the impact of blood transfusion and erythropoiesis stimulating agent therapy on renal transplant wait time. Methods: We retrospectively analyzed all adult patients listed for first deceased donor kidney transplantation at two transplant centers in Central Pennsylvania between 2004 and 2008. The exposures of interest were blood transfusion and erythropoietin stimulating agent therapy. Cox proportional hazards were used to model time to deceased donor kidney transplant. Results: Among 407 patients listed for transplant, 84 received a deceased donor kidney during a median follow-up of 26.3 months. In an adjusted Cox proportional hazards model, with erythropoiesis stimulating agent and transfusion both treated as time-dependent exposures, UNOS inactive status at listing date (hazard ratio [HR] 0.81; 95% CI 0.73 - 0.89; P < 0.001) and transfusion during the wait list period (HR 0.27; 95% CI 0.11 - 0.69; P = 0.01) independently predicted longer transplant wait time. Erythropoiesis stimulating agent use prior to or after transplant wait listing date did not independently predict wait time. Conclusion: Blood transfusion while waitlisted for kidney transplant is strongly associated with prolonged wait time.
A classification of spectral populations observed in HF radar backscatter from the E region auroral electrojets
S. E. Milan ,M. Lester
Annales Geophysicae (ANGEO) , 2001,
Abstract: Observations of HF radar backscatter from the auroral electrojet E region indicate the presence of five major spectral populations, as opposed to the two predominant spectral populations, types I and II, observed in the VHF regime. The Doppler shift, spectral width, backscatter power, and flow angle dependencies of these five populations are investigated and described. Two of these populations are identified with type I and type II spectral classes, and hence, are thought to be generated by the two-stream and gradient drift instabilities, respectively. The remaining three populations occur over a range of velocities which can greatly exceed the ion acoustic speed, the usual limiting velocity in VHF radar observations of the E region. The generation of these spectral populations is discussed in terms of electron density gradients in the electrojet region and recent non-linear theories of E region irregularity generation. Key words. Ionosphere (ionospheric irregularities)
Simultaneous observations at different altitudes of ionospheric backscatter in the eastward electrojet
S. E. Milan,M. Lester
Annales Geophysicae (ANGEO) , 2003,
Abstract: A common feature of evening near-range ionospheric backscatter in the CUTLASS Iceland radar field of view is two parallel, approximately L-shell-aligned regions of westward flow which are attributed to irregularities in the auroral eastward electrojet region of the ionosphere. These backscatter channels are separated by approximately 100–200 km in range. The orientation of the CUTLASS Iceland radar beams and the zonally aligned nature of the flow allows an approximate determination of flow angle to be made without the necessity of bistatic measurements. The two flow channels have different azimuthal variations in flow velocity and spectral width. The nearer of the two regions has two distinct spectral signatures. The eastern beams detect spectra with velocities which saturate at or near the ion-acoustic speed, and have low spectral widths (less than 100 m s–1), while the western beams detect lower velocities and higher spectral widths (above 200 m s–1). The more distant of the two channels has only one spectral signature with velocities above the ion-acoustic speed and high spectral widths. The spectral characteristics of the backscatter are consistent with E-region scatter in the nearer channel and upper-E-region or F-region scatter in the further channel. Temporal variations in the characteristics of both channels support current theories of E-region turbulent heating and previous observations of velocity-dependent backscatter cross-section. In future, observations of this nature will provide a powerful tool for the investigation of simultaneous E- and F-region irregularity generation under similar (nearly co-located or magnetically conjugate) electric field conditions. Key words. Auroral ionosphere · Ionospheric irregularities · Plasma convection
The relationship between electric fields, conductances and currents in the high-latitude ionosphere: a statistical study using EISCAT data
J. A. Davies,M. Lester
Annales Geophysicae (ANGEO) , 2003,
Abstract: The relationship between electric fields, height-integrated conductivities and electric currents in the high-latitude nightside electrojet region is known to be complex. The tristatic nature of the EISCAT UHF radar facility provides an excellent means of exploring this interrelationship as it enables simultaneous estimates to be made of the full electric field vector and the ionospheric Hall and Pedersen conductances, further allowing the determination of both field-perpendicular electric current components. Over 1300 h of common programme observations by the UHF radar system provide the basis of a statistical study of electric fields, conductances and currents in the high-latitude ionosphere, from which preliminary results are presented. Times at which there is significant solar contribution to the ionospheric conductances have been excluded by limiting the observations according to solar zenith angle. Initial results indicate that, in general, the times of peak conductance, identified from the entire set of EISCAT observations, do not correspond to the times of the largest electric field values; the relative contribution of ionospheric conductance and electric field to the electrojet currents therefore depends critically on local time, a conclusion which corroborates work by previous authors. Simultaneous measurements confirm a tendency for a decrease in both Hall and Pedersen conductances to be accompanied by an increase in the electric field, at least for moderate and large electric field value, a tendency which is also identified to some extent in the ratio of the conductances, which acts as an indicator of the energy of precipitating particles. Key words. Ionosphere (auroral ionosphere; electric fields and currents)
SABRE observations of Pi2 pulsations: case studies
E. G. Bradshaw,M. Lester
Annales Geophysicae (ANGEO) , 2003,
Abstract: The characteristics of substorm-associated Pi2 pulsations observed by the SABRE coherent radar system during three separate case studies are presented. The SABRE field of view is well positioned to observe the differences between the auroral zone pulsation signature and that observed at mid-latitudes. During the first case study the SABRE field of view is initially in the eastward electrojet, equatorward and to the west of the substorm-enhanced electrojet current. As the interval progresses, the western, upward field-aligned current of the substorm current wedge moves westward across the longitudes of the radar field of view. The westward motion of the wedge is apparent in the spatial and temporal signatures of the associated Pi2 pulsation spectra and polarisation sense. During the second case study, the complex field-aligned and ionospheric currents associated with the pulsation generation region move equatorward into the SABRE field of view and then poleward out of it again after the third pulsation in the series. The spectral content of the four pulsations during the interval indicate different auroral zone and mid-latitude signatures. The final case study is from a period of low magnetic activity when SABRE observes a Pi2 pulsation signature from regions equatorward of the enhanced substorm currents. There is an apparent mode change between the signature observed by SABRE in the ionosphere and that on the ground by magnetometers at latitudes slightly equatorward of the radar field of view. The observations are discussed in terms of published theories of the generation mechanisms for this type of pulsation. Different signatures are observed by SABRE depending on the level of magnetic activity and the position of the SABRE field of view relative to the pulsation generation region. A twin source model for Pi2 pulsation generation provides the clearest explanation of the signatures observed.
Mechanisms of HIV Transcriptional Regulation and Their Contribution to Latency
Gillian M. Schiralli Lester,Andrew J. Henderson
Molecular Biology International , 2012, DOI: 10.1155/2012/614120
Abstract: Long-lived latent HIV-infected cells lead to the rebound of virus replication following antiretroviral treatment interruption and present a major barrier to eliminating HIV infection. These latent reservoirs, which include quiescent memory T cells and tissue-resident macrophages, represent a subset of cells with decreased or inactive proviral transcription. HIV proviral transcription is regulated at multiple levels including transcription initiation, polymerase recruitment, transcription elongation, and chromatin organization. How these biochemical processes are coordinated and their potential role in repressing HIV transcription along with establishing and maintaining latency are reviewed. 1. Introduction A critical step in the HIV life cycle is transcriptional regulation of the integrated provirus. Robust transcription assures that sufficient mRNA and genomic RNA are produced for efficient virus assembly and infectivity. Repression of HIV transcription leads to the establishment of HIV latency, which creates repositories for infectious and drug-resistant viruses that reemerge upon treatment failure or interruption [1–4]. The existence of long-lived stable HIV reservoirs was demonstrated by the rebound of virus replication following highly active antiretroviral therapy (HAART) interruption [5–8]. These latent reservoirs, which include quiescent memory T cells, tissue-resident macrophages [9, 10], and potentially hematopoietic stem cells [11], although this is still controversial [12], represent long-lived subsets of cells with decreased or inactive proviral transcription. In general, studies with chronically and acutely infected cells show that mutations in Tat [13, 14], absence of cellular transcription factors [15–18], miRNA machinery [19, 20], and proviral integration into transcriptionally silent sites contribute to postintegration latency [21, 22]. Although there may not be a common mechanism that promotes HIV latency, it is critical to understand the molecular events that establish and maintain latency if strategies to reduce or purge HIV from latent reservoirs are to be devised [9, 23, 24]. HIV transcription is regulated at multiple levels including transcription initiation, polymerase recruitment, transcriptional elongation, and chromatin organization. How these events are coordinated and their role in HIV latency will be reviewed. In particular, mechanisms that contribute to repressing HIV transcription will be highlighted. 2. LTR and Transcription Factors Although viral accessory proteins, such as Vpr, and putative elements within the HIV
Mother-infant consultation during drug treatment: Research and innovative clinical practice
CF Zachariah Boukydis, Barry M Lester
Harm Reduction Journal , 2008, DOI: 10.1186/1477-7517-5-6
Abstract: A sequential cohort model was used to assign participants to 1. NNNS consultation versus 2. standard care. The effects of NNNS consultation were evaluated using the Parenting Stress Index and NNNS summary scores.Participants in the NNNS consultation condition had significantly less stress overall, and less stress related to infant behavior than participants in standard care. There were no differences in infant behavior on the NNNS Summary scores.The implications for NNNS consultation in drug treatment programs is outlined. The importance of prevention/intervention to establish satisfactory mother-infant interaction in recovery programs which include a central parenting component is indicated.In the past fifteen year, there have been marked changes in drug treatment services for women (Finkelstein, 1996 [1]; Homan et al, 1993[2]; Clayson, Berkowitz & Brindis, 1995[3]; Lester, Twomey, Boukydis, 2000[4]). One central feature to these services is the recognition of challenges that many women of childbearing age face to progress in recovery, and as mothers, to grow and mature as parents with their children. There is an identified need to integrate parenting support and education into traditional drug treatment programs (Weissman et al, 1995[5]; Jones, 2006 [6]). Programs which combine drug treatment and parenting services are more likely to retain women in treatment and decrease the likelihood of relapse (Roberts & Nishimoto, 1996[7]; Szuster et al, 1996[8]; Kaltenbach & Finnegan, 1998[9]; Jones, 2006[6]). There has also been a need to integrate and evaluate new models derived from fields such as child development, applied developmental psychology and infant mental health (Lester, Affleck. Boukydis, Freier & Boris, 1996[10]; Sameroff, 2004[11]). The central focus of this paper is on the use of neonatal assessment to consult with mothers and infants in order to improve maternal ability to read the unique signals of their infant, provide a satisfactory beginning to early p
Substance use during pregnancy: time for policy to catch up with research
Barry M Lester, Lynne Andreozzi, Lindsey Appiah
Harm Reduction Journal , 2004, DOI: 10.1186/1477-7517-1-5
Abstract: The purpose of this review is to summarize policy research findings in the area of maternal prenatal substance abuse to (1) inform and advance this field, (2) identify future research needs, (3) inform policy making and (4) identify implications for policy. As a review, this is a systematic analysis of existing data (findings) on maternal drug use during pregnancy for determining the best policy among the alternatives for dealing with drug using mothers and their children. We will address issues of efficacy (which policies work?), economics (how much does it cost?) and politics (who is it for or against?). For new policies we will also consider how they fit with existing policies or laws, the social impact, ethical issues and the feasibility of implementation and administration.The issue of substance abuse is one that has perpetually plagued society. The complexities surrounding addiction are not easily overcome. These complexities are even more defined in cases of substance abuse by pregnant women, an issue that has been pushed to the forefront of the public consciousness over the course of the past 20 years. Maternal prenatal substance abuse is defined as chronic use of alcohol and/or other drugs [1]. The acronym AOD is often used to describe the generic problem of alcohol and other drugs. However, AOD is not specific to mothers and includes both prenatal and postnatal use as well as use by men. This review will encompass the three main types of addictive substances used during pregnancy: alcohol, tobacco and illegal drugs (ATID). Maternal Alcohol, Tobacco and Illegal Drugs (MATID) will be used to describe maternal use of these substances during pregnancy that threatens the well being of the child.Rising cocaine use and the emergence of crack cocaine use in the 1980s created a public outcry and redress and served to shine the spotlight on this issue. One of the goals of this review is to see how what we learned from the cocaine controversy can be applied to issues
Analysis and Experimental Verification of Losses in a Concentrated Wound Interior Permanent Magnet Machine
Rukmi Dutta;Lester Chong;Fazlur M. Rahman
PIER B , 2013, DOI: 10.2528/PIERB12110715
Abstract: It is well known that additional space harmonics in the air-gap magnetomotive force (mmf) distribution of the concentrated non-overlapping windings (CW) cause additional losses in the machine. This is especially so for machines used for traction applications where the machine requires to operate over its rated speed and frequency. In this paper, the authors investigates losses present in an interior permanent magnet (IPM) machine with CW designed to achieve a very wide field weakening range. Losses were quantified analytically and also using finite element methods. Loss estimations were experimentally verified in a constructed prototype machine. Based on the analysis, key losses were identified. The optimization process to minimize these losses and of improving efficiency were discussed in details. The segregation of the losses in the studied machine indicates that the losses in the magnet are much smaller compared to the rotor and stator core losses caused by the slot harmonics. Therefore, core loss minimization techniques for this type of machine will involve reduction of slot harmonics. Also, copper loss is found to be the most dominating component of the total loss. Hence, copper loss minimization should be part of the design optimization process.
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