Correlation function of spin noise due to atomic diffusion

We use paramagnetic Faraday rotation to study spin noise spectrum from unpolarized Rb vapor in a tightly focused probe beam in the presence of N$_2$ buffer gas. We derive an analytical form for the diffusion component of the spin noise time-correlation function in a Gaussian probe beam. We also obtain analytical forms for the frequency spectrum of the spin noise in the limit of a tightly focused or a collimated Gaussian beam in the presence of diffusion. In particular, we find that in a tightly focused probe beam the spectral lineshape can be independent of the buffer gas pressure. Experimentally, we find good agreement between the calculated and measured spin noise spectra for N$_2$ gas pressures ranging from 56 to 820 torr.Comment: 6 pages, 4 figure

Closed form Greens functions for general sources and stratified media

Cataloged from PDF version of article.The closed-form Green's functions of the vector and scalar potentials in the spatial domain are presented for the sources of horizontal electric, magnetic, and vertical electric, magnetic dipoles embedded in general, multilayer, planar media. First, the spectral domain Green's functions in an arbitrary layer are derived analytically from the Green's functions in the source layer by using a recursive algorithm. Then, the spatial domain Green's functions are obtained by adding the contributions of the direct terms, surface waves, and complex images approximated by the Generalized Pencil of Functions Method (GPOF). In the derivations, the main emphasis is to put these closed-form representations in a suitable form for the solution of the mixed potential integral equation (MPIE) by the method of moments in a general three-dimensional geometry. The contributions of this paper are: 1) providing the complete set of closed-form Green's functions in spectral and spatial domains for general stratified media; 2) using the GPOF method, which is more robust and less noise sensitive, in the derivation of the closed-form spatial domain Green's functions; and 3) casting the closed-form Green's functions in a form to provide efficient applications of the method of moments. © 1995 IEE

Mutual coupling of printed elements on a cylindrically layered structure using closed-form Green's functions

A hybrid method to calculate mutual coupling of electric or magnetic current elements on a cylindrically layered structure using closed-form Green's functions is presented. When rho = rho' and phi is not very close to phi', closed-form Green's functions are employed in the calculation of MoM matrix entries. When both rho = rho' and phi = phi', series representation of the spectral domain Green's functions do not converge, therefore closed-form Green's functions can not be employed. In that case MoM matrix entries are evaluated using the proposed hybrid method. The technique is applied to both printed dipoles and slots placed on a layered cylindrical structures. The computational efficiency of the analysis of mutual coupling of printed elements on cylindrically layered geometries is increased with the use of proposed hybrid method which employs closed-form Green's functions

Femtotesla direct magnetic gradiometer using a single multipass cell

We describe a direct gradiometer using optical pumping with opposite circular polarization in two $^{87}$Rb atomic ensembles within a single multipass cell. A far-detuned probe laser undergoes a near-zero paramagnetic Faraday rotation due to the intrinsic subtraction of two contributions exceeding 3.5 rad from the highly-polarized ensembles. We develop analysis methods for the direct gradiometer signal and measure a gradiometer sensitivity of $10.1$ fT/cm$\sqrt{\mathrm{Hz}}$. We also demonstrate that our multipass design, in addition to increasing the optical depth, provides a fundamental advantage due to the significantly reduced effect of atomic diffusion on the spin noise time-correlation, in excellent agreement with theoretical estimate.Comment: 5 pages, 4 figure

Association of ECG characteristics with clinical and echocardiographic outcome to CRT in a non-LBBB patient population

Purpose: Effectiveness of cardiac resynchronization therapy (CRT) in patients without left bundle branch block (non-LBBB) QRS morphology is limited. Additional selection criteria are needed to identify these patients. Methods: Seven hundred ninety consecutive patients with non-LBBB morphology, who received a CRT-device in 3 university centers in the Netherlands, were selected. Pre-implantation 12-lead ECGs were evaluated on morphology, duration, and area of the QRS complex, as well as on PR interval, left ventricular activation time (LVAT), and the presence of fragmented QRS (fQRS). Association of these ECG features with the primary endpoint: a combination of left ventricular assist device (LVAD) implantation, cardiac transplantation and all-cause mortality, and secondary endpoint—echocardiographic reduction of left ventricular end-systolic volume (LVESV)—were evaluated. Results: The primary endpoint occurred more often in non-LBBB patients with with PR interval ≥ 230ms, QRS area < 109μVs, and with fQRS. Multivariable regression analysis showed independent associations of QRS area (HR 2.33 [1.44, 3.77], p = 0.001) and PR interval (HR 2.03 [1.51, 2.74], p < 0.001) only. Mean LVESV reduction was significantly lower in patients with baseline RBBB, QRS duration < 150 ms, PR interval ≥ 230 ms, and in QRS area < 109 μVs. Multivariable regression analyses only showed significant associations between QRS area ≥ 109 μVs (OR 2.00 [1.09, 3.66] p = 0.025) and probability of echocardiographic response to CRT. Conclusions: In the heterogeneous non-LBBB patient population, QRS area and PR prolongation rather than traditional QRS duration and morphology are associated to both clinical and echocardiographic outcomes of CRT

Usporedba zrcalnog modela i modela prijenosnih linija u analizi horizontalne žičane strukture iznad dvoslojnog tla

The paper presents comparison between two approximate models of energized horizontal thin-wire conductors above two-layer soil. The formulation is posed in frequency domain by using two approaches. The first one is based on quasi-static image theory within Mixed Potential Integral Equation. The second one is based on transmission line theory with approximation of per unit length parameters. The authors compare currents computed by the both approximate models of a center fed wire to establish the computation errors over a wide frequency range. The main objective is to validate the proposed image and transmission line models for various lengths of wire conductors, and various cases of low and high conductivities of two-layer soil. The verification of the results is done by comparison with exact model based on full-wave theory. Detailed parametric analysis clearly illustrate validity domain and problems when using both approximate models with respect to their use in practical EMC studies.U radu je prikazana usporedba dviju približnih modela analize pobuđenog horizontalnog tankog žičanog vodiča iznad dvoslojnog tla. Formulacija problema je izvedena u frekvencijskoj domeni pomoću dva pristupa. Prvi pristup se temelji na kvazi-statičkom zrcalnom modelu unutar integralne jednadžbe s mješovitim potencijalima. Drugi se temelji na teoriji prijenosnih linija s aproksimacijom jediničnih parametara. Autori su usporedili distribucije struje izračunate s pomoću obje približne metode kako bi odredili pogrešku metoda u širokom rasponu frekvencija. Glavni cilj bio je potvrditi predloženi zrcalni i linijski model za različite duljine žičanog vodiča i razne slučajeve niske i visoke vodljivosti slojeva tla. Provjera rezultata obavljena je usporedbom s modelom bez aproksimacija temeljenog na punovalnoj teoriji. Detaljna parametarska analiza jasno pokazuju valjanosti domene i vrste problema uz korištenje obje približne metode s obzirom na njihovu primjenu u praktičnim EMC razmatranjima

Descriptors of Posidonia oceanica meadows: Use and application

The conservation of the coastal marine environment requires the possession of information that enables the global quality of the environment to be evaluated reliably and relatively quickly. The use of biological indicators is often an appropriate method. Seagrasses in general, and Posidonia oceanica meadows in particular, are considered to be appropriate for biomonitoring because of their wide distribution, reasonable size, sedentary habit, easy collection and abundance and sensitivity to modifications of littoral zone. Reasoned management, on the scale of the whole Mediterranean basin, requires standardized methods of study, to be applied by both researchers and administrators, enabling comparable results to be obtained. This paper synthesises the existing methods applied to monitor P. oceanica meadows, identifies the most suitable techniques and suggests future research directions. From the results of a questionnaire, distributed to all the identified laboratories working on this topic, a list of the most commonly used descriptors was drawn up, together with the related research techniques (e.g. standardization, interest and limits, valuation of the results). It seems that the techniques used to study meadows are rather similar, but rarely identical, even though the various teams often refer to previously published works. This paper shows the interest of a practical guide that describes, in a standardized way, the most useful techniques enabling P. oceanica meadows to be used as an environmental descriptor. Indeed, it constitutes the first stage in the process. (c) 2005 Elsevier Ltd. All rights reserved.Peer reviewe