717 research outputs found
Towards an ultra efficient kinetic scheme. Part I: basics on the BGK equation
In this paper we present a new ultra efficient numerical method for solving
kinetic equations. In this preliminary work, we present the scheme in the case
of the BGK relaxation operator. The scheme, being based on a splitting
technique between transport and collision, can be easily extended to other
collisional operators as the Boltzmann collision integral or to other kinetic
equations such as the Vlasov equation. The key idea, on which the method
relies, is to solve the collision part on a grid and then to solve exactly the
transport linear part by following the characteristics backward in time. The
main difference between the method proposed and semi-Lagrangian methods is that
here we do not need to reconstruct the distribution function at each time step.
This allows to tremendously reduce the computational cost of the method and it
permits for the first time, to the author's knowledge, to compute solutions of
full six dimensional kinetic equations on a single processor laptop machine.
Numerical examples, up to the full three dimensional case, are presented which
validate the method and assess its efficiency in 1D, 2D and 3D
Principals and Professional Learning Communities: Breaking Down Barriers to Effective Response to Intervention in Secondary Schools
In the past decade, there has been a call for reform to improve adolescent literacy achievement. Response to Intervention (RTI) is a widely employed multi-tiered intervention system designed to identify and support the academic needs of at-risk students. Despite the success of RTI for younger students, there is little research documenting ways to effectively implement the model in secondary schools. This article identifies barriers that interfere with RTI implementation and highlights strategies to avoid failure. In particular, we emphasize the need for administrative support when initiating RTI and suggest building Professional Learning Communities (PLCs) to ensure teachers are offered the time to collaborate on planning, implementing, and assessing the effects of RTI. Keywords: administration, differentiated instruction, literacy, professional development, secondary education, special education DOI: 10.7176/JEP/12-23-03 Publication date:August 31st 202
Archive data base and handling system for the Orbiter flying qualities experiment program
The OFQ archives data base and handling system assembled as part of the Orbiter Flying Qualities (OFQ) research of the Orbiter Experiments Program (EOX) are described. The purpose of the OFQ archives is to preserve and document shuttle flight data relevant to vehicle dynamics, flight control, and flying qualities in a form that permits maximum use for qualified users. In their complete form, the OFQ archives contain descriptive text (general information about the flight, signal descriptions and units) as well as numerical time history data. Since the shuttle program is so complex, the official data base contains thousands of signals and very complex entries are required to obtain data. The OFQ archives are intended to provide flight phase oriented data subsets with relevant signals which are easily identified for flying qualities research
Sustained intraatrial reentrant tachycardia: Clinical, electrocardiographic and electrophysiologic characteristics and long-term follow-up
Although intraatrial reentry has been traditionally listed as a mechanism for supraventricular tachycardia, few reports describing the clinical features of this arrhythmia exist. Nineteen patients with a clinical history of sustained supraventricular tachycardia were diagnosed as having intraatrial reentrant tachycardia. Seventeen (89%) patients of the 19 had underlying structural heart disease and 17 had echocardiographic evidence of atrial enlargement; the mean left ventricular ejection fraction was 51 ± 16%. A history of concomitant atrial fibrillation or flutter was present in 13 patients (68%). The mean atrial cycle length during tachycardia was 326 ± 57 ms (range 260 to 460). Fourteen patients had 1:1 atrioventricular (AV) conduction during tachycardia, of whom 50% had an RP7RR' ratio >0.5.Intravenous adenosine (dose range 37.5 to 150 ”g/kg) and verapamil (dose range 5 to 10 mg) had no effect on atrial tachycardia cycle length in 13 of 14 and 9 of 9 patients, respectively, despite induction of second degree AV block. Type la antiarrhythmic drugs achieved longterm suppression of intraatrial reentrant tachycardia in only 6 patients, whereas amiodarone (326 ± 145 mg/day) was successful in 11 patients during a 32 ± 20 month follow-up period. The remaining two patients and one patient who later developed amiodarone toxicity either progressed to (n = 1) or had (n = 2) catheter-induced high grade AV block and were treated with long-term ventricular pacing.It is concluded that intraatrial reentrant tachycardia is often associated with structural heart disease, particularly of types that cause atrial abnormalities, but left ventricular dysfunction is not a requisite finding. Other arrhythmias are frequently observed in these patients. This arrhythmia responds poorly to type la antiarrhythmic drugs, but is effectively treated with amiodarone. Catheter ablation of the AV junction offers a therapeutic option for patients who are refractory to medical therapy
The Moment Guided Monte Carlo method for the Boltzmann equation
In this work we propose a generalization of the Moment Guided Monte Carlo
method developed in [11]. This approach permits to reduce the variance of the
particle methods through a matching with a set of suitable macroscopic moment
equations. In order to guarantee that the moment equations provide the correct
solutions, they are coupled to the kinetic equation through a non equilibrium
term. Here, at the contrary to the previous work in which we considered the
simplified BGK operator, we deal with the full Boltzmann operator. Moreover, we
introduce an hybrid setting which permits to entirely remove the resolution of
the kinetic equation in the limit of infinite number of collisions and to
consider only the solution of the compressible Euler equation. This
modification additionally reduce the statistical error with respect to our
previous work and permits to perform simulations of non equilibrium gases using
only a few number of particles. We show at the end of the paper several
numerical tests which prove the efficiency and the low level of numerical noise
of the method.Comment: arXiv admin note: text overlap with arXiv:0908.026
DNA-methylation dependent regulation of embryo-specific 5S ribosomal DNA cluster transcription in adult tissues of sea urchin Paracentrotus lividus
We have previously reported a molecular and cytogenetic characterization of three different
5S rDNA clusters in the sea urchin Paracentrotus lividus and recently, demonstrated the presence of
high heterogeneity in functional 5S rRNA. In this paper, we show some important distinctive data on 5S
rRNA transcription for this organism. Using Single Strand Conformation Polymorphism (SSCP)
analysis, we demonstrate the existence of two classes of 5S rRNA, one which is embryo-specific and
encoded by the smallest (700bp) cluster and the other which is expressed at every stage and encoded
by longer clusters (900 and 950bp). We also demonstrate that the embryo-specific class of 5S rRNA is
expressed in oocytes and embryonic stages and is silenced in adult tissue and that this phenomenon
appears to be due exclusively to DNA methylation, as indicated by sensitivity to 5-azacytidine, unlike
Xenopus where this mechanism is necessary but not sufficient to maintain the silenced status
Psychological assessment in pathological gamblers treated with escitalopram
Pathological Gambling (PG) is classified as a "Disorder of Impulse Control", but due to similarities with drug addiction is frequently described as a drug-free addiction (Potenza et al., 2012). PG is conceptualized as a behavioural addiction because of its neurobiologic, neurophysiologic and psychological features. Current therapeutical
approaches seem unsatisfactory as they do not achieve definitive positive outcomes. Considering the well known
psycopathological comorbidities, PG represents both a social (impact on relatives money/life) and a sanitary cost, in terms of pharmacological and psychological support. The compulsive behaviour detectable in PG, is a disease with neurophysiopathological basis now fairly well-defined which affects particularly vulnerable people. PG is linked to important changes in brain systems such as the prefrontal cortex, the nucleus accumbens, the endogenous opioid system and the extended amygdale. Recent fMRI studies associate PG with blunted mesolimbic activation to non-specific rewards, whereas increased prefrontal cortex, anterior cingulate and ventral striatum activation is observed during gambling-related
cue-exposure paradigms. Several neuropsychological studies show higher impulsivity in PG (Odlaug BL. et al., 2013) that, together with specific psychopathological symptoms, such as anxiety and depressed mood, characterize different PG subtypes (Blaszczynski A, Nower L. 2002). Impulsivity transcends multiple psychiatric disorders and is thought to be central to impulse control disorders such as PG. Furthermore, many PGs suffers from depression and decreased mood
Hydrographic Properties and Inferred Circulation Over the Northeastern Shelves of the Gulf of Mexico During Spring to Midsummer of 1998
A hydrographic cruise was conducted 5-16 May 1998 over the northeastern shelves of the Gulf of Mexico, Observed distributions of temperature, salinity, oxygen, and nutrients were consonant with prior occurrences of upwelling, particularly near the head of DeSoto Canyon. Shipboard, moored, and satellite observations indicated these upwelling events were related to the presence of an anticyclonic circulation feature over the canyon. In addition, several cool water events occurred during spring in the nearshore region west of Pensacola; these may be attributed to atmospheric effects. High river discharges from rivers west of the Apalachicola during winter and spring likely resulted in the extensive surface distributions of low-salinity water observed from Mississippi Sound to Cape San Bias during the cruise. The combination of cool bottom temperatures and relatively low surface salinities over the inshore shelf west of Cape San Bias, with the usual seasonal warming, resulted in enhanced vertical stability. This stability likely inhibited vertical mixing and contributed to the development of the relatively low concentrations of dissolved oxygen observed in the bottom waters
Use of a regional wall motion score to enhance risk stratification of patients receiving an implantable cardioverter-defibrillator
AbstractObjectives. We postulated that preoperative assessment of both regional wall motion and left ventricular ejection fraction would serve as an accurate prognostic indicator of long-term cardiac mortality and functional outcome in patients treated with an implantable cardioverter-defibrillator.Background. Long-term cardiac mortality has remained high in patients receiving an implantable cardioverter-defibrillator. The ability to risk stratify patients before defibrillator implantation is becoming increasingly important from a medical and economic standpoint.Methods. The hypothesis was retrospectively tested in 74 patients who had received an implantable cardioverterdefibrillator. Left ventricular ejection fraction and regional wall motion score, derived from centerline chord motion analysis, were calculated for each patient from the preoperative right anterior oblique contrast ventriculogram. Wall motion score was the only significant independent predictor of long-term cardiac mortality and functional status by multivariate analysis because of its enhanced prognostic capability in patients with an ejection fraction in the critical range of 30% to 40%.Results. Patients with an ejection fraction >40% had a 3-year cardiac mortality rate of 0% compared with 25% for those with an ejection fraction of 30% to 40% and 48% for those with an ejection fraction <30% (p < 0.05). Similarly, 75% of patients with an ejection fraction >40% were in New York Heart Association functional class I or II during long-term follow-up compared with 59% of those with an ejection fraction 30% to 40% and 29% of those with an ejection fraction <30%. Among patients with an ejection fraction of 30% to 40%, those with a wall motion score >16% had a 3-year cardiac mortality rate of 0% compared with 71% of those with a wall motion score †16% (p = 0.002). In addition, 86% of patients with a wall motion score >16% were in functional class I or II during long-term follow-up compared with 13% of those with a wall motion score â€16% (p = 0.001).Conclusions. Long-term cardiac mortality and functional outcome in patients receiving an implantable cardioverterdefibrillator can be predicted if the left ventricular ejection fraction and regional wall motion score are measured preoperatively
First records of the mourning gecko (Lepidodactylus lugubris Duméril and Bibron, 1836), common house gecko (Hemidactylus frenatus in Duméril, 1836), and Tokay gecko (Gekko gecko Linnaeus, 1758) on Curaçao, Dutch Antilles, and remarks on their Caribbean distributions
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