A systematic analysis of the discrete conservation properties of non-dissipative, central-difference approximations of the compressible Navier–Stokes equations is reported. A generalized splitting of ...the nonlinear convective terms is considered, and energy-preserving formulations are fully characterized by deriving a two-parameter family of split forms. Previously developed formulations reported in literature are shown to be particular members of this family; novel splittings are introduced and discussed as well. Furthermore, the conservation properties yielded by different choices for the energy equation (i.e. total and internal energy, entropy) are analyzed thoroughly. It is shown that additional preserved quantities can be obtained through a suitable adaptive selection of the split form within the derived family. Local conservation of primary invariants, which is a fundamental property to build high-fidelity shock-capturing methods, is also discussed in the paper. Numerical tests performed for the Taylor–Green Vortex at zero viscosity fully confirm the theoretical findings, and show that a careful choice of both the splitting and the energy formulation can provide remarkably robust and accurate results.
•Energy-preserving split forms in compressible flow equations are studied.•A novel two-parameter family of energy-preserving splittings is derived.•A dynamic splitting procedure with optimal conservation properties is proposed.
ABSTRACT We present new nonlinear, time-dependent convective hydrodynamical models of RR Lyrae stars computed assuming a constant helium-to-metal enrichment ratio and a broad range in metal ...abundances (Z = 0.0001-0.02). The stellar masses and luminosities adopted to construct the pulsation models were fixed according to detailed central He-burning horizontal-branch evolutionary models. The pulsation models cover a broad range in stellar luminosity and effective temperatures and the modal stability is investigated for both fundamental (FU) and first overtone polsators (FOs). We predict the topology of the instability strip (IS) as a function of the metal content and new analytical relations for the edges of the IS in the observational plane. Moreover, a new analytical relation to constrain the pulsation mass of double pulsators as a function of the period ratio and the metal content is provided. We derive new Period-Radius-Metallicity relations for FU and FO pulsators. They agree quite well with similar empirical and theoretical relations in the literature. From the predicted bolometric light curves, transformed into optical (UBVRI) and near-infrared (NIR; JHK) bands, we compute the intensity-averaged mean magnitudes along the entire pulsation cycle and in turn new and homogenous metal-dependent (RIJHK) Period-Luminosity relations. Moreover, we compute new dual and triple-band optical, optical-NIR, and NIR Period-Wesenheit-Metallicity relations. Interestingly, we find that the optical Period-W(V, B-V) is independent of the metal content and that the accuracy of individual distances is a balance between the adopted diagnostics and the precision of photometric and spectroscopic data sets.
Sperm morphology is regarded as a significant prognostic factor for fertilization, as abnormal sperm structure is one of the most common factors in male infertility. Furthermore, obtaining accurate ...morphological information is an important issue with strong implications in zoo-technical industries, for example to perform sorting of species X from species Y. A challenging step forward would be the availability of a fast, high-throughput and label-free system for the measurement of physical parameters and visualization of the 3D shape of such biological specimens. Here we show a quantitative imaging approach to estimate simply and quickly the biovolume of sperm cells, combining the optical tweezers technique with digital holography, in a single and integrated set-up for a biotechnology assay process on the lab-on-a-chip scale. This approach can open the way for fast and high-throughput analysis in label-free microfluidic based "cytofluorimeters" and prognostic examination based on sperm morphology, thus allowing advancements in reproductive science.
The application of pseudo-symplectic Runge–Kutta methods to the incompressible Navier–Stokes equations is discussed in this work. In contrast to fully energy-conserving, implicit methods, these are ...explicit schemes of order p that preserve kinetic energy to order q, with q>p. Use of explicit methods with improved energy-conservation properties is appealing for convection-dominated problems, especially in case of direct and large-eddy simulation of turbulent flows. A number of pseudo-symplectic methods are constructed for application to the incompressible Navier–Stokes equations and compared in terms of accuracy and efficiency by means of numerical simulations.
Treatments that stimulate neuronal excitability enhance motor performance after stroke. cAMP-response-element binding protein (CREB) is a transcription factor that plays a key role in neuronal ...excitability. Increasing the levels of CREB with a viral vector in a small pool of motor neurons enhances motor recovery after stroke, while blocking CREB signaling prevents stroke recovery. Silencing CREB-transfected neurons in the peri-infarct region with the hM4Di-DREADD blocks motor recovery. Reversing this inhibition allows recovery to continue, demonstrating that by manipulating the activity of CREB-transfected neurons it is possible to turn off and on stroke recovery. CREB transfection enhances remapping of injured somatosensory and motor circuits, and induces the formation of new connections within these circuits. CREB is a central molecular node in the circuit responses after stroke that lead to recovery from motor deficits.
ABSTRACT We present new multiband (UBVI) time-series data of helium burning variables in the Carina dwarf spheroidal galaxy. The current sample includes 92 RR Lyrae-six of them are new ...identifications-and 20 Anomalous Cepheids, one of which is new identification. The analysis of the Bailey diagram shows that the luminosity amplitude of the first overtone component in double-mode variables is located along the long-period tail of regular first overtone variables, while the fundamental component is located along the short-period tail of regular fundamental variables. This evidence further supports the transitional nature of these objects. Moreover, the distribution of Carina double-mode variables in the Petersen diagram (P1/P0 versus P0) is similar to metal-poor globulars (M15, M68), to the dwarf spheroidal Draco, and to the Galactic Halo. This suggests that the Carina old stellar population is metal-poor and affected by a small spread in metallicity. We use trigonometric parallaxes for five field RR Lyrae stars to provide an independent estimate of the Carina distance using the observed reddening free Period-Wesenheit PW, (BV) relation. Theory and observations indicate that this diagnostic is independent of metallicity. We found a true distance modulus of = 20.01 0.02 (standard error of the mean) 0.05 (standard deviation) mag. We also provided independent estimates of the Carina true distance modulus using four predicted PW relations (BV, BI, VI, BVI) and we found: = (20.08 0.007 0.07) mag, = (20.06 0.006 0.06) mag, = (20.07 0.008 0.08) mag, and = (20.06 0.006 0.06) mag. Finally, we identified more than 100 new SX Phoenicis stars that together with those already known in the literature (340) make Carina a fundamental laboratory for constraining the evolutionary and pulsation properties of these transitional variables.
Radio-frequency and Helicon Plasma Thrusters have emerged as viable electric propulsion systems due to their high plasma density, thrust density, and useful life. Helicon Plasma Thruster (HPT) is a ...very attractive technology because it could use many propellants and does not require hollow cathodes or grids, overcoming their associated critical erosion problem and extending the thruster’s lifetime to some tens of thousands of hours. Despite the fact that high-power HPTs have reached 30% efficiency in laboratory configurations, sophisticated numerical models are required for a deeper understanding of the main plasma phenomena and for the preliminary design to increase the very low HPT’s efficiency (3–7%) typical of the low-power class thrusters. The paper focuses on the development of a model for the low-medium power range (50–2000 W) of HPTs design. Starting from Lafleur’s model, it has been improved with the hypothesis of neutral gas being expelled at the real thruster’s wall operative temperature (300–600 K) in place of the more frequent laboratory temperature assumption (300 K). This hypothesis affects total thrust and specific impulse by about 10%. A parametric analysis of the slenderness ratio (chamber length-to-radius) has been conducted. The results showed that slender configurations lead to higher efficiencies. Downstream from the numerical model validation, a tool for the global design has been built with the Particle Swarm Optimization (PSO) technique that leads to optimal thruster configuration. This tool has been used to design a 4 mN HPT tuning the PSO in order to minimize the dimensions and the weight according to the assigned mission constraints (i.e., power, thrust, and weight). A total efficiency of 10.4% results.
Although migraineurs appear in general to be hypersensitive to external stimuli, they maybe also have increased daytime sleepiness and complain of fatigue. Neurophisiological studies between attacks ...have shown that for a number of different sensory modalities the migrainous brain is characterised by a lack of habituation of evoked responses. Whether this is due to increased cortical hyperexcitability, possibly due to decreased inhibition, or to an abnormal responsivity of the cortex due a decreased preactivation level remains disputed. Studies using transcranial magnetic stimulation in particular have yielded contradictory results. We will review here the available data on cortical excitability obtained with different methodological approaches in patients over the migraine cycle. We will show that these data congruently indicate that the sensory cortices of migraineurs react excessively to repetitive, but not to single, stimuli and that the controversy above hyper- versus hypo-excitability is merely a semantic misunderstanding. Describing the migrainous brain as ‘hyperresponsive’ would fit most of the available data. Deciphering the precise cellular and molecular underpinnings of this hyperresponsivity remains a challenge for future research. We propose, as a working hypothesis, that a thalamo-cortical dysrhythmia might be the culprit.
Rare maternally inherited duplications at 15q11-13 are observed in ~1% of individuals with an autism spectrum disorder (ASD), making it among the most common causes of ASD. 15q11-13 comprises a ...complex region, and as this copy number variation encompasses many genes, it is important to explore individual genotype-phenotype relationships. Cytoplasmic FMR1-interacting protein 1 (CYFIP1) is of particular interest because of its interaction with Fragile X mental retardation protein (FMRP), its upregulation in transformed lymphoblastoid cell lines from patients with duplications at 15q11-13 and ASD and the presence of smaller overlapping deletions of CYFIP1 in patients with schizophrenia and intellectual disability. Here, we confirm that CYFIP1 is upregulated in transformed lymphoblastoid cell lines and demonstrate its upregulation in the post-mortem brain from 15q11-13 duplication patients for the first time. To investigate how increased CYFIP1 dosage might predispose to neurodevelopmental disease, we studied the consequence of its overexpression in multiple systems. We show that overexpression of CYFIP1 results in morphological abnormalities including cellular hypertrophy in SY5Y cells and differentiated mouse neuronal progenitors. We validate these results in vivo by generating a BAC transgenic mouse, which overexpresses Cyfip1 under the endogenous promotor, observing an increase in the proportion of mature dendritic spines and dendritic spine density. Gene expression profiling on embryonic day 15 suggested the dysregulation of mammalian target of rapamycin (mTOR) signaling, which was confirmed at the protein level. Importantly, similar evidence of mTOR-related dysregulation was seen in brains from 15q11-13 duplication patients with ASD. Finally, treatment of differentiated mouse neuronal progenitors with an mTOR inhibitor (rapamycin) rescued the morphological abnormalities resulting from CYFIP1 overexpression. Together, these data show that CYFIP1 overexpression results in specific cellular phenotypes and implicate modulation by mTOR signaling, further emphasizing its role as a potential convergent pathway in some forms of ASD.
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