1,354,445 research outputs found
Schumann's resonances: A particular example of a spherical resonant cavity
No full textThe resonances between the Earth as one boundary and the ionosphere as the other, known as Schumann's resonances, represent an interesting example of a spherical cavity. We consider a simple model in which the boundaries behave as perfect conductors and then take into account the finite conductivity of the boundaries. Numerical results are obtained for both models and compared with available data. Good agreement is shown to exist between the analytical results and the experimental values when finite conductivity of the walls is considered.Fil: Ciappina, Marcelo Fabián. Universidad Nacional del Sur. Departamento de Física; ArgentinaFil: Febbo, Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Física; Argentin
A finite extensibility nonlinear oscillator
No full textThe dynamics of a finite extensibility nonlinear oscillator (FENO) is studied analytically by means of two different approaches: a generalized decomposition method (GDM) and a linearized harmonic balance procedure (LHB). From both approaches, analytical approximations to the frequency of oscillation and periodic solutions are obtained, which are valid for a large range of amplitudes of oscillation. Within the generalized decomposition method, two different versions are presented, which provide different kinds of approximate analytical solutions. In the first version, it is shown that the truncation of the perturbation solution up to the third order provides a remarkable degree of accuracy for almost the whole range of amplitudes. The second version, which expands the nonlinear term in Taylor's series around the equilibrium point, exhibits a little lower degree of accuracy, but it supplies an infinite series as the approximate solution. On the other hand, a linearized harmonic balance method is also employed, and the comparison between the approximate period and the exact one (numerically calculated) is slightly better than that obtained by both versions of the GDM. In general, the agreement between the results obtained by the three methods and the exact solution (numerically integrated) for amplitudes (A) between 0 < A ≤ 0.9 is very good both for the period and the amplitude of oscillation. For the rest of the amplitude range (0.9 < A < 1), an exponentially large L2 error demonstrates that all three approximations do not represent a good description for the FENO, and higher order perturbation solutions are needed instead. As a complement, very accurate asymptotic representations of the period are provided for the whole range of amplitudes of oscillation. © 2011 Elsevier Inc. All rights reserved.Fil: Febbo, Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad Nacional del Sur. Departamento de Física; Argentin
Clinical and biochemical response to neridronate treatment in a patient with osteoporosis-pseudoglioma syndrome (OPPG)
No full textOsteoporosis-pseudoglioma syndrome (OPPG) is a rare autosomal recessive syndrome characterized by juvenile-onset osteoporosis and ocular abnormalities due to a low-density lipoprotein receptor-related protein 5 (LRP5) gene mutation. Treatment with bisphosphonates, particularly with pamidronate and risedronate, has been reported to be of some efficacy in this condition. We report on a patient with OPPG due to an LRP5 gene mutation, who showed an encouraging response after a 36-month period of neridronate therapy. We report a case of a patient treated with bisphosphonates. Bisphosphonates should be administered in OPPG patients as a first-line therapy during early childhood
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Harmonic response of a class of finite extensibility nonlinear oscillators
No full textFinite extensibility oscillators are widely used to simulate those systems which can not be extended to infinity. For example, they are used when modelling the bonds between molecules in a polymer or DNA molecule or when simulating filaments of non-Newtonian liquids. In this work, the dynamic behavior of a harmonically driven finite extensibility oscillator is presented and studied. To this end, the harmonic balance method is applied to determine the amplitude-frequency and the amplitude-phase equations. The distinguishable feature in this case is the bending of the amplitude-frequency curve to the frequency axis, making it to approach asymptotically to the limit of maximum elongation of the oscillator, which physically represents the impossibility for the systemto reach this limit. Also, the stability condition which defines stable and unstable steady-states solutions is derived. The study of the effect of the system parameters in the response reveals that a decreasing value of damping coefficient or an increasing value of excitation amplitude leads to the appearance of a multi-valued response and to the existence of a jump phenomenon. In this sense, the critical amplitude of the excitation, which refers to here as a certain value of external excitation that results in the occurrence of jump phenomena, is also derived. Numerical experiments to observe the effects of the system parameters on the frequency-amplitude response are performed to compare them to analytical calculations. For a low value of damping coefficient or a high value of excitation amplitude the agreement is poor for low frequencies but good for high frequencies.It is demonstrated that the disagreement is caused by neglecting the higher-order harmonics in the analytical formulation. These higher-order harmonics, which appear as distinguishable peaks at certain values in the frequency response curves, are possible to calculate considering not the linearized frequency of the oscillator but its actual frequency which is strongly amplitude-dependent. On the other side, for a high value of damping coefficient or a low value of excitation amplitude, the agreement between numerical and analytical calculations is excellent. For these cases, the system is prevented to explore large amplitudes of vibration and, therefore, thenonlinearity is not too much manifested.Fil: Febbo, Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin
WRITING INSTRUMENT, SYSTEM AND METHOD FOR TRANSPARENT MONITORING AND ANALYSIS OF WRITING
No full textThe present invention relates to a writing instrument comprising: - a writing element comprises a writing end configured for depositing a writing materiai on a support; - a plurality of sensors comprising at least: - a force sensor configured to measure a force applied to said writing element, and - a movement sensor configured to measure movement of the instrument in a three- dimensionai space; - a communication unit configured to exchange data with a remote device via a wireless communication channel; - a control unit connected to the plurality of sensors and to the communication unit configured to control said plurality of sensors and said communication unit in order to transmit to the remote device the measures provided of the plurality of sensors in presence of a connection between the communication unit and the remote device, - a memory unit connected to the control unit and configured to store one or more measures of said plurality of sensors, and - a hollow casing
Placental site trophoblastic tumor on endometrial polyp: a case report
No full textPlacental site trophoblastic tumor (PSTT) is the least common form of gestational trophoblastic disease (GTD), and is biologically different from other forms of GTD. There is a wide clinical spectrum of presentation and behavior ranging from a benign condition to an aggressive disease with a fatal outcome. The authors document a case of PSTT on an endometrial polyp. A 51-year-old woman had abnormal vaginal bleeding for the duration of two months. Her past history included a vaginal delivery in 1998. Her physical examination was normal. Tumor markers were at normal levels. Serum beta- human chorionic gonadotropin (hCG) level was 19 mIU/ml and human placental lactogen (hPL) level was in the normal range. The patient underwent an operative hysteroscopy. On examination the uterine cavity appeared to be occupied by a pedunculated polypoid neoformation measuring about 2.5 cm in diameter which was removed and later determined to be a PSTT. There were occasional mitotic figures (0-1/10 high power field). The patient underwent hysterectomy and bilateral salpingo-oophorectomy. The patient has no evidence of disease six months after surgery. The authors conclude that a high mitotic count and atypical undifferentiated pathological features are significant poor prognostic factors for survival in PSTT. Hysterectomy represents the gold standard of treatment in all cases of disease confined to the uteru
Reduced levels of poly(ADP-ribosyl)ation result in chromatin compaction and hypermethylation as shown by cell-by-cell computer assisted quantitative analysis
No full textThe unmethylated status of the CpG islands is important for gene expression of correlated housekeeping genes since it is well known that their methylation inhibits transcription process. An interesting question that has been discussed but not solved is how the CpG islands maintain their characteristic unmethylated status even though they are rich in CpG dinucleotides. Our previous in vitro and in vivo research has shown that poly(ADP-ribosyl)ation is involved in protecting CpG dinucleotides from full methylation in genomic DNA and that a block of poly(ADP-ribosyl)ation is also involved in modifying the methylation pattern in the promoter region of Htf9 housekeeping gene. In this study we locked for cytological evidence that in the absence of an active poly(ADP-ribosyl)ation the DNA methylation pattern in L929 and NIH/3T3 mouse fibroblast cell lines is altered. For this purpose, differences in the methylation levels of interphase nuclei from control and treated cultures of two murine cell lines preincubated with 2 mM 3-aminobenzamide, an inhibitor of poly(ADP-ribosyl)ation, were measured in individual cells after indirect immunolabeling with anti-5MeC antibodies. The quantitative analysis allowed us to demonstrate that blocking of the poly(ADP-ribosyl)ation results in a higher number, size, and density of antibody binding regions in treated cells when compared to the controls. Analogously, sequential Giemsa staining and indirect immunolabeling of the same slides showed the heterochromatic regions colocalized with the extended methyl-rich domains
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