Temperature Effects in Acoustic Resonators

This paper deals with problems of nonlinear standing waves in axisymetrically shaped acoustic resonators where a mean temperature is distributed along the axis

Solution of the Burgers Equation in the Time Domain

This paper deals with a theoretical description of the propagation of a finite amplitude acoustic waves. The theory based on the homogeneous Burgers equation of the second order of accuracy is presented here. This equation takes into account both nonlinear effects and dissipation. The method for solving this equation, using the well-known Cole-Hopf transformation, is presented. Two methods for numerical solution of these equations in the time domain are presented. The first is based on the simple Simpson method, which is suitable for smaller Goldberg numbers. The second uses the more advanced saddle point method, and is appropriate for large Goldberg numbers

Propagation of Quasi-plane Nonlinear Waves in Tubes

This paper deals with possibilities of using the generalized Burgers equation and the KZK equation to describe nonlinear waves in circular ducts. A new method for calculating of diffraction effects taking into account boundary layer effects is described. The results of numerical solutions of the model equations are compared. Finally, the limits of validity of the used model equations are discussed with respect to boundary conditions and the radius of the circular duct. The limits of applicability of the KZK equation and the GBE equation for describing nonlinear waves in tubes are discussed

Carbon dioxide fluxes increase from day to night across European streams

Globally, inland waters emit over 2 Pg of carbon per year as carbon dioxide, of which the majority originates from streams and rivers. Despite the global significance of fluvial carbon dioxide emissions, little is known about their diel dynamics. Here we present a large-scale assessment of day- and night-time carbon dioxide fluxes at the water-air interface across 34 European streams. We directly measured fluxes four times between October 2016 and July 2017 using drifting chambers. Median fluxes are 1.4 and 2.1 mmol m−2 h−1 at midday and midnight, respectively, with night fluxes exceeding those during the day by 39%. We attribute diel carbon dioxide flux variability mainly to changes in the water partial pressure of carbon dioxide. However, no consistent drivers could be identified across sites. Our findings highlight widespread day-night changes in fluvial carbon dioxide fluxes and suggest that the time of day greatly influences measured carbon dioxide fluxes across European streams

Propagation of Quasi-plane Nonlinear Waves in Tubes

This paper deals with possibilities of using the generalized Burgers equation and the KZK equation to describe nonlinear waves in circular ducts. A new method for calculating of diffraction effects taking into account boundary layer effects is described. The results of numerical solutions of the model equations are compared. Finally, the limits of validity of the used model equations are discussed with respect to boundary conditions and the radius of the circular duct. The limits of applicability of the KZK equation and the GBE equation for describing nonlinear waves in tubes are discussed

Test-retest reproducibility of neurochemical profiles with short-echo, single-voxel MR spectroscopy at 3T and 7T

Purpose To determine the test-retest reproducibility of neurochemical concentrations obtained with a highly optimized, short-echo, single-voxel proton MR spectroscopy (MRS) pulse sequence at 3T and 7T using state-of-the-art hardware. Methods A semi-LASER sequence (echo time = 26–28 ms) was used to acquire spectra from the posterior cingulate and cerebellum at 3T and 7T from six healthy volunteers who were scanned four times weekly on both scanners. Spectra were quantified with LCModel. Results More neurochemicals were quantified with mean Cramér-Rao lower bounds (CRLBs) ≤20% at 7T than at 3T despite comparable frequency-domain signal-to-noise ratio. Whereas CRLBs were lower at 7T (P < 0.05), between-session coefficients of variance (CVs) were comparable at the two fields with 64 transients. Five metabolites were quantified with between-session CVs ≤5% at both fields. Analysis of subspectra showed that a minimum achievable CV was reached with a lower number of transients at 7T for multiple metabolites and that between-session CVs were lower at 7T than at 3T with fewer than 64 transients. Conclusion State-of-the-art MRS methodology allows excellent reproducibility for many metabolites with 5-min data averaging on clinical 3T hardware. Sensitivity and resolution advantages at 7T are important for weakly represented metabolites, short acquisitions, and small volumes of interest

Feasibility and reproducibility of neurochemical profile quantification in the human hippocampus at 3 T

Hippocampal dysfunction is known to be associated with several neurological and neuropsychiatric disorders such as Alzheimer's disease, epilepsy, schizophrenia and depression; therefore, there has been significant clinical interest in studying hippocampal neurochemistry. However, the hippocampus is a challenging region to study using (1) H MRS, hence the use of MRS for clinical research in this region has been limited. Our goal was therefore to investigate the feasibility of obtaining high-quality hippocampal spectra that allow reliable quantification of a neurochemical profile and to establish inter-session reproducibility of hippocampal MRS, including reproducibility of voxel placement, spectral quality and neurochemical concentrations. Ten healthy volunteers were scanned in two consecutive sessions using a standard clinical 3 T MR scanner. Neurochemical profiles were obtained with a short-echo (T(E) = 28 ms) semi-LASER localization sequence from a relatively small (~4 mL) voxel that covered about 62% of the hippocampal volume as calculated from segmentation of T1 -weighted images. Voxel composition was highly reproducible between sessions, with test-retest coefficients of variation (CVs) of 3.5% and 7.5% for gray and white matter volume fraction, respectively. Excellent signal-to-noise ratio (~54 based on the N-acetylaspartate (NAA) methyl peak in non-apodized spectra) and linewidths (~9 Hz for water) were achieved reproducibly in all subjects. The spectral quality allowed quantification of NAA, total choline, total creatine, myo-inositol and glutamate with high scan-rescan reproducibility (CV ≤ 6%) and quantification precision (Cramér-Rao lower bound, CRLB < 9%). Four other metabolites, including glutathione and glucose, were quantified with scan-rescan CV below 20%. Therefore, the highly optimized, short-echo semi-LASER sequence together with FASTMAP shimming substantially improved the reproducibility and number of quantifiable metabolites relative to prior reports. In addition, the between-session variation in metabolite concentrations, as well as CRLB, was lower than the between-subject variation of the concentrations for most metabolites, indicating that the method has the sensitivity to detect inter-individual differences in the healthy brain

Sexting : grado de aceptación en los adolescentes de Cataluña

El sexting es la práctica que se dedica al envío de imágenes y vídeos de contenido sexual a través de las redes sociales y aplicaciones móviles. Este estudio pretende observar el grado de aceptación del sexting entre los adolescentes de Cataluña, y en que medida esta normalizada esta práctica en su día a día. La muestra de esta investigación la componen 103 jóvenes de 14 a 18 años, los cuales fueron seleccionados aleatoriamente a través de un método de difusión del cuestionario de esta investigación. Este cuestionario está compuesto de preguntas cerradas y preguntas adaptadas a una escala tipo Likert, el cual valoraba su conocimiento y comprensión, vulnerabilidad e influencia y su juicio respecto al sexting. En los resultados se expuso que los jóvenes utilizan el sexting como práctica en sus relaciones de pareja y sexuales, y pese a conocer lo que significa, la mayoría no conocen la palabra técnica "sexting".Sexting is the action of sending pictures or videos with a sexual content though the social networks and the mobile applications. This study pretends to observe the stage of acceptation about the sexting through the teenagers from Catalonia, and if it is normalized or not. The sample is composed by 103 teenagers of ages understood between 14 and 18 years, which were chosen from spreading the questionnaire of this investigation. This questionnaire is composed by closed questions and questions adapted to a Likert scale, which values the knowledge and comprehension, vulnerability and influence and their judgement about sexting. In the results we found that teenagers use sexting as a practice in their relationships and sexual relationships and, despite knowing the meaning, the majority does not know the technical word "sexting

Czech National Guillain-Barré Syndrome Registry

Úvod: Guillainův-Barrého syndrom je akutní zánětlivá autoimunitní polyradikuloneuropatie patřící mezi vzácnější neurologická onemocnění, nicméně po téměř úplné eradikaci poliomyelitidy je celosvětově nejčastější příčinou akutně vzniklé chabé paralýzy. Registr funguje od roku 2012 a poskytuje prospektivně zaznamenávaná data. Cíl: Cílem registru je sledování klinického profi lu, léčby a šestiměsíční prognózy nemocných s Guil lainovým-Bar rého syndromem. Metodika: Data zadávají osoby pověřené neuromuskulárními centry. Klinický průběh je hodnocen na základě GBS disability scale a svalové síly pro obličejové svalstvo a svalstvo končetin. Vyšetření je provedeno při přijetí pa cienta k hospitalizaci, před léčbou, ihned po léčbě, za 1 měsíc a za 6 měsíců od ukončení léčby. Výsledky: V registru bylo aznamenáno celkem 272 případů, u 137 z nich jsou k dispozici kompletní data za 6 měsíců. Z těchto 137 pa cientů bylo 52 léčeno intravenózním lidským imunoglobulinem a 85 výměn nou plazmaferézou. Dobrého výsledného klinického stavu po 6 měsících dosáhlo celkem 85 % pa cientů. Reziduální těžký neurologický defi cit přetrvával po 6 měsících u 11 % pa cientů. Šest pa cientů zemřelo. Nezaznamenali jsme rozdíl v účinnosti imunoglobulinu a plazmaferézy v celém souboru, v podskupině nejtěžších pa cientů či ve vztahu k pohlaví. Závěr: Centralizace péče a dodržování standardů péče vedou k dobré prognóze nemocných s Guil lainovým-Bar rého syndromem srovnatelné s relevantními zdroji.Introduction: The Guillain-Barré syndrome is an acute infl ammatory autoimmune polyradiculoneuropathy and belongs among rare neurologic diseases. Since poliomyelitis has been almost completely eliminated, it is currently the most frequent cause of acute fl accid paralysis worldwide. The registry was formed in the Czech Republic in 2012 and is an important source of prospectively recorded data. Aim: The goal of the registry is to follow up the clinical profi le, treatment and 6-month prognosis of Guillain-Barré syndrome patients. Methods: The data are collected prospectively by persons delegated by neuromuscular centres in the Czech Republic. The clinical course is assessed on the basis of the GBS disability scale and muscle strength according to the Medical Research Council sum score for facial muscles and extremity muscles. Detailed clinical investigation is done on admission, before the treatment, immediately after the treatment, 1 month and 6 months after the end of the treatment. Results: We enrolled a total 272 cases of Guillain-Barré syndrome patients in the period from 1st January 2012 to 17th August 2016. We have complete data for 6 months in 137 of them. 52 were treated with intravenous human immunoglobulin and 85 with plasma exchange. A good clinical outcome after 6 months (ability to walk unassisted) was achieved in 85% of patients. Severe residual neurological defi cit persisted after 6 months in 11% of patients. The remaining 6 patients died. We did not fi nd any diff erence in the effi ciency of immunoglobulin vs. plasma exchange in the whole group, in the subgroup of the severely disabled patients and according to sex. Conclusion: Medical care centralisation and adherence to the standard of care lead to a good clinical outcome in Guillain-Barré syndrome patients, which is comparable with relevant sources