Association Between Serum 25-Hydroxyvitamin D Concentration and Optic Chiasm Volume

International audienc

Association Between Hypovitaminosis D and Late Stages of Age-Related Macular Degeneration: A Case-Control Study

International audienc

Abnormal increase in urinary aquaporin-2 excretion in response to hypertonic saline in essential hypertension

<p>Abstract</p> <p>Background</p> <p>Dysregulation of the expression/shuttling of the aquaporin-2 water channel (AQP2) and the epithelial sodium channel (ENaC) in renal collecting duct principal cells has been found in animal models of hypertension. We tested whether a similar dysregulation exists in essential hypertension.</p> <p>Methods</p> <p>We measured urinary excretion of AQP2 and ENaC β-subunit corrected for creatinine (u-AQP2_CR, u-ENaC_β-CR), prostaglandin E2 (u-PGE₂) and cyclic AMP (u-cAMP), fractional sodium excretion (FE_Na), free water clearance (C_H2O), as well as plasma concentrations of vasopressin (AVP), renin (PRC), angiotensin II (Ang II), aldosterone (Aldo), and atrial and brain natriuretic peptide (ANP, BNP) in 21 patients with essential hypertension and 20 normotensive controls during 24-h urine collection (baseline), and after hypertonic saline infusion on a 4-day high sodium (HS) diet (300 mmol sodium/day) and a 4-day low sodium (LS) diet (30 mmol sodium/day).</p> <p>Results</p> <p>At baseline, no differences in u-AQP2_CRor u-ENaC_β-CRwere measured between patients and controls. U-AQP2_CRincreased significantly more after saline in patients than controls, whereas u-ENaC_β-CRincreased similarly. The saline caused exaggerated natriuretic increases in patients during HS intake. Neither baseline levels of u-PGE₂, u-cAMP, AVP, PRC, Ang II, Aldo, ANP, and BNP nor changes after saline could explain the abnormal u-AQP2_CRresponse.</p> <p>Conclusions</p> <p>No differences were found in u-AQP2_CRand u-ENaC_β-CRbetween patients and controls at baseline. However, in response to saline, u-AQP2_CRwas abnormally increased in patients, whereas the u-ENaC_β-CRresponse was normal. The mechanism behind the abnormal AQP2 regulation is not clarified, but it does not seem to be AVP-dependent.</p> <p>Clinicaltrial.gov identifier</p> <p><a href="http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=00345124">NCT00345124</a>.</p

Quelques aspects des écoulements presque horizontaux à deux dimensions en plan et non permanent, application aux estuaires

This paper deals with an investigation of near-horizontal free surface flows with a view to finding digital computer solutions for hydraulics problems in coastal waters. PART I. - This sets up the equations for the problem, with the following basic assumptions : Uniform velocity distribution along a vertical. Hydrostatic pressure distribution. Little bed and surface slope. The unknowns to be determined in terms of space variables x, y and the time variable t are as follows : h = depth of water u, v, = velocity components [Eq. (1), (2), (3)] or : z : free surface level ; U: uh ; V : vh [Eq. (I), (II), (III)]. PART II. - In this part, the above equations are made linear, which holds good if, taking the mean free surface level as the datum level, Z remains small compared to depth D = - Zf (where Zf is the bed level) and if water column displacements are small compared to the considered area [Eq. (I a), (II a), (III a)]. Where these assumptions no longer apply in full, equations can be considered which are no longer purely linear, in which only the convection terms are ignored. PART III. - In this part, the characteristics theory is applied to the quasi-linear system (I), (II), (III) in order to show up the boundery conditions required for the calculation, and to establish a numerical solution scheme. After stating the equations in form (1 b), (II b), (III b) and then in matrix form (4), the condition is sought for which the unknown vector R. = (Z, U, V) is determined near a surface (S) whose eqnation is t = Φ (x, y) and on which R (x, y, t) = R [x, y, Φ (x, y)] = R0 (x, y) are given. This condition requires that the determinant of system (4), (6), (7) whose unknowns are ∂R/∂x, ∂R/∂y, ∂R/∂t be different from zero. ∂R/∂x and ∂R/∂y are eliminated for simplification and equation (8) is obtained, in which the determinant to be considered-called the 'charaeteristic determinant' -is det A = det (I - A p - Ayq), where p = ∂Φ/∂x and q = ∂Φ/∂y. If this determinant is zero, relations (9) and (10) are obtained between the director cosines of the normal to surface (S). Surfaces (S) satisfying these relationships form two families of surfaces referred to as 'characteristic surfaces'. It can he established by local inspection that tangent planes t = px + qy to these surfaces at an assumed origin have the following envelope : First family : the cone whose equation is (11) or (11') ; Second family : the straight line which is the locus of circular sections of the above cone through planes t = constant. As the determinant of system (8) is zero the latter is impossible or inedeterminate. It is indeterminate if the equations of (8) are not linearly independent : if (8) is written down in the form AX = Ythere is a vector t such that tA = 0 and tY = 0. The result of this is (l2), i.e. a linear combination of equations (4). Hence, this relationship is a compatibility condition which is satisfied by the unknowns on the characteristic surfaces. Vector t and the corresponding charactcristic relationship arc made explicit for each family of surfaces by the subsequent ca1culations; equations (13') and (14) emerge, which can be written as (13') and (14') in wich only internal differentiation operators for the considered surface appear. These relationships connect a space point (x, y, t) to neighbouring points belonging to characteristic surface passing through that point ; the latter, therefore, is related to the envelope of these surfaces. The notions of a 'domain of influence' and 'domain of dependence of a point' emerge, i.e, the inside of the future (or past) characteristic cone having that point at its apex ; the state of the point is determined by that of the points within its 'domain of dependence' and it enters into the determination of points belonging to its 'domain of influence' , The final paragraph of Part III gives the results of the application of the characteristics theory to the linear equations ; for the first family, the envelope of the characteristic surfaces is a cone whose equation is (15), and it is the axis of this cone for the second family. The characteristic relationships are (16) and (17), or (16') and (17'). PART IV. - Discusses boundary conditions. System (I), (II), (III), is to be solved in a cylindrical domain D = Ω x [0, T]. As the unknown vector R = (Z, U, V), is given in Ω for t = 0 (initial conditions), it is necessary to introduce boundary conditions at each instant t0 on the contour Γ of Ω. There are at least as many of these conditions as there are characteristic half-planes (t < t0) originating from outside D and based on Γ X [0, T], Except for shooting flow, therefore, one or two conditions must be set, depending on whether the flow is from or into Ω. If the equations to be solved are in linear cone only one boundary condition is required, as fol1ows : Along the coast : an impermeability condition: Wn = 0, where W is a velocity vector and n is normal to the shore. Along maritime or permeable boundaries : normal discharge or water level vs. time, or a relationship between the three unknowns. In particular, this relationship can represent an incident wave. PART V. - Two explicit numerical integration schemes are suggested. One is derived from the characterietics theory and relies on the relationships holding good on the characteristic surfaces of the first family (tangent planes to the cone) for θ = 0, + π, ± (π / 2). These relationships are approximated by finite difference equations concerning values of vector R at the mesh points in a predetennined mesh network. This seheme is stable if the Courant-Friedrichs-Levy condition is satisfied, The second-more conventional-scheme relies on centred differences to calculate unknowns at staggered points but is governed by stricter stability conditions

Reducing Sound Impact From Multibeam Bathymetry

Multibeam bathymetry systems use the travel time of acoustic pulses as observable to determine the depth of the seafloor. In order to provide appropriate echo quality necessary for depth determination and seafloor shape recording, a high acoustic source level is needed. The main factors affecting the sound level of the emitted sonar pulse during the travel through the water column are geometrical spreading, absorption and the backscattering strength of the seabed. The reception threshold of the acoustic receiver determines the sound level needed to detect the acoustic pulse. Common deep sea multibeam systems use the determined depth as an indication to control the source level necessary for the successive ping.Lowering the transmission level of hydroacoustic sources is a general demand to reduce the impact of sonar signals on the marine life. In order to protect marine mammals we studied the capability of RV Polarstern's Hydrosweep multibeam system. However, reducing the source level finally limits the ability of accurate depth determination. The recent upgrade of Hydrosweep provides the possibility to adjust the source level based on the echo quality. Automatic and manual controls can be used to reduce the source level while achieving a given limit of data quality for selected beam angles. We present first results of this feasibility study focusing on the applicability of different methods used for reducing the acoustic source level. The influence of the source level reduction on data quality and accuracy is evaluated on the basis of terrain models derived from a test survey in a special calibration area in the Bay of Biscay