3,459 research outputs found

    On polynomially integrable domains in Euclidean spaces

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    Let DD be a bounded domain in Rn,\mathbb R^n, with smooth boundary. Denote VD(ω,t), ωSn1,tR,V_D(\omega,t), \ \omega \in S^{n-1}, t \in \mathbb R, the Radon transform of the characteristic function χD\chi_{D} of the domain D,D, i.e., the (n1)(n-1)- dimensional volume of the intersection DD with the hyperplane {xRn:=t}.\{x \in \mathbb R^n: =t \}. If the domain DD is an ellipsoid, then the function VDV_D is algebraic and if, in addition, the dimension nn is odd, then V(ω,t)V(\omega,t) is a polynomial with respect to t.t. Whether odd-dimensional ellipsoids are the only bounded smooth domains with such a property? The article is devoted to partial verification and discussion of this question

    Firms' Main Market, Human Capital and Wages

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    Recent international trade literature emphasizes two features in characterizing the current patterns of trade: efficiency heterogeneity at the firm level and quality differentiation. This paper explores human capital and wage differences across firms in that context. We build a partial equilibrium model predicting that firms selling in more-remote markets employ higher human capital and pay higher wages to employees within each education group. The channel linking these variables is firms’ endogenous choice of quality. Predictions are tested using Spanish employer-employee matched data that classify firms according to four main destination markets: local, national, European Union, and rest of the World. Employees’ average education is increasing in the remoteness of firm’s main output market. Market–destination wage premia are large, increasing in the remoteness of the market, and increasing in individual education. These results suggest that increasing globalization may play a significant role in raising wage inequality within and across education groups

    How a plantar pressure-based, tongue-placed tactile biofeedback modifies postural control mechanisms during quiet standing

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    The purpose of the present study was to determine the effects of a plantar pressure-based, tongue-placed tactile biofeedback on postural control mechanisms during quiet standing. To this aim, sixteen young healthy adults were asked to stand as immobile as possible with their eyes closed in two conditions of No-biofeedback and Biofeedback. Centre of foot pressure (CoP) displacements, recorded using a force platform, were used to compute the horizontal displacements of the vertical projection the centre of gravity (CoGh) and those of the difference between the CoP and the vertical projection of the CoG (CoP-CoGv). Altogether, the present findings suggest that the main way the plantar pressure-based, tongue-placed tactile biofeedback improves postural control during quiet standing is via both a reduction of the correction thresholds and an increased efficiency of the corrective mechanism involving the CoGh displacements

    On the dynamics of WKB wave functions whose phase are weak KAM solutions of H-J equation

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    In the framework of toroidal Pseudodifferential operators on the flat torus Tn:=(R/2πZ)n\Bbb T^n := (\Bbb R / 2\pi \Bbb Z)^n we begin by proving the closure under composition for the class of Weyl operators Opw(b)\mathrm{Op}^w_\hbar(b) with simbols bSm(Tn×Rn)b \in S^m (\mathbb{T}^n \times \mathbb{R}^n). Subsequently, we consider Opw(H)\mathrm{Op}^w_\hbar(H) when H=12η2+V(x)H=\frac{1}{2} |\eta|^2 + V(x) where VC(Tn;R)V \in C^\infty (\Bbb T^n;\Bbb R) and we exhibit the toroidal version of the equation for the Wigner transform of the solution of the Schr\"odinger equation. Moreover, we prove the convergence (in a weak sense) of the Wigner transform of the solution of the Schr\"odinger equation to the solution of the Liouville equation on Tn×Rn\Bbb T^n \times \Bbb R^n written in the measure sense. These results are applied to the study of some WKB type wave functions in the Sobolev space H1(Tn;C)H^{1} (\mathbb{T}^n; \Bbb C) with phase functions in the class of Lipschitz continuous weak KAM solutions (of positive and negative type) of the Hamilton-Jacobi equation 12P+xv±(P,x)2+V(x)=Hˉ(P)\frac{1}{2} |P+ \nabla_x v_\pm (P,x)|^2 + V(x) = \bar{H}(P) for PZnP \in \ell \Bbb Z^n with >0\ell >0, and to the study of the backward and forward time propagation of the related Wigner measures supported on the graph of P+xv±P+ \nabla_x v_\pm

    The importance of cytosolic glutamine synthetase in nitrogen assimilation and recycling

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    Glutamine synthetase assimilates ammonium into amino acids, thus it is a key enzyme for nitrogen metabolism. The cytosolic isoenzymes of glutamine synthetase assimilate ammonium derived from primary nitrogen uptake and from various internal nitrogen recycling pathways. In this way, cytosolic glutamine synthetase is crucial for the remobilization of protein-derived nitrogen. Cytosolic glutamine synthetase is encoded by a small family of genes that are well conserved across plant species. Members of the cytosolic glutamine synthetase gene family are regulated in response to plant nitrogen status, as well as to environmental cues, such as nitrogen availability and biotic/abiotic stresses. The complex regulation of cytosolic glutamine synthetase at the transcriptional to post-translational levels is key to the establishment of a specific physiological role for each isoenzyme. The diverse physiological roles of cytosolic glutamine synthetase isoenzymes are important in relation to current agricultural and ecological issues

    Long-term efficacy of orthokeratology contact lens wear in controlling the progression of childhood myopia

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    Purpose: The primary outcome of this study is to compare the axial length growth of white European myopic children wearing orthokeratology contact lenses (OK) to a control group (CT) over a 7-year period. Methods: Subjects 6–12 years of age with myopia −0.75 to −4.00DS and astigmatism ≤1.00DC were prospectively allocated OK or distance single-vision spectacles (SV) correction. Measurements of axial length (Zeiss IOLMaster), corneal topography, and cycloplegic refraction were taken at 6-month intervals over a 2-year period. Subjects were invited to return to the clinic approximately 5 years later (i.e., 7 years after the beginning of the study) for assessment of their ocular refractive and biometric components. The CT consisted of 4 SV and 12 subjects who switched from SV to soft contact lens wear after the initial 2 years of SV lens wear. Changes in axial length relative to baseline over a 7-year period were compared between groups. Results: Fourteen and 16 subjects from the OK and CT groups, respectively, were examined 6.7 ± 0.5 years after the beginning of the study. Statistically significant changes in the axial length were found over time and between groups (both p <0.001), but not for the time*group interaction (p = 0.125). The change in the axial length for the OK group was 22% (p = 0.328), 42% (p = 0.007), 40% (p = 0.020), 41% (p = 0.013), and 33% (p = 0.062) lower than the CT group following 6, 12, 18, 24, and 84 months of lens wear, respectively. Conclusion: A trend toward a reduction in the rate of axial elongation of the order of 33% was found in the OK group in comparison to the CT group following 7 years of lens wear
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