Swiss clinical practice guidelines on field cancerization of the skin.

Actinic keratosis (AK) affects millions of people worldwide, and its prevalence continues to increase. AK lesions are caused by chronic ultraviolet radiation exposure, and the presence of two or more AK lesions along with photodamage should raise the consideration of a diagnosis of field cancerization. Effective treatment of individual lesions as well as field cancerization is essential for good long-term outcomes. The Swiss Registry of Actinic Keratosis Treatment (REAKT) Working Group has developed clinical practice guidelines for the treatment of field cancerization in patients who present with AK. These guidelines are intended to serve as a resource for physicians as to the most appropriate treatment and management of AK and field cancerization based on current evidence and the combined practical experience of the authors. Treatment of AK and field cancerization should be driven by consideration of relevant patient, disease, and treatment factors, and appropriate treatment decisions will differ from patient to patient. Prevention measures and screening recommendations are discussed, and special considerations related to management of immunocompromised patients are provided.

Evaluation of organ-specific peripheral doses after 2-dimensional, 3-dimensional and hybrid intensity modulated radiation therapy for breast cancer based on Monte Carlo and convolution/superposition algorithms: implications for secondary cancer risk assessment.

To make a comprehensive evaluation of organ-specific out-of-field doses using Monte Carlo (MC) simulations for different breast cancer irradiation techniques and to compare results with a commercial treatment planning system (TPS). Three breast radiotherapy techniques using 6MV tangential photon beams were compared: (a) 2DRT (open rectangular fields), (b) 3DCRT (conformal wedged fields), and (c) hybrid IMRT (open conformal+modulated fields). Over 35 organs were contoured in a whole-body CT scan and organ-specific dose distributions were determined with MC and the TPS. Large differences in out-of-field doses were observed between MC and TPS calculations, even for organs close to the target volume such as the heart, the lungs and the contralateral breast (up to 70% difference). MC simulations showed that a large fraction of the out-of-field dose comes from the out-of-field head scatter fluence (>40%) which is not adequately modeled by the TPS. Based on MC simulations, the 3DCRT technique using external wedges yielded significantly higher doses (up to a factor 4-5 in the pelvis) than the 2DRT and the hybrid IMRT techniques which yielded similar out-of-field doses. In sharp contrast to popular belief, the IMRT technique investigated here does not increase the out-of-field dose compared to conventional techniques and may offer the most optimal plan. The 3DCRT technique with external wedges yields the largest out-of-field doses. For accurate out-of-field dose assessment, a commercial TPS should not be used, even for organs near the target volume (contralateral breast, lungs, heart).

Calculation of the magnetic field penetration depth for high-Tc cuprate superconductors based on the Interlayer Pair Tunneling model /

In this work, the magnetic field penetration depth for high-Tc cuprate superconductors is calculated using a recent Interlayer Pair Tunneling (ILPT) model proposed by Chakravarty, Sudb0, Anderson, and Strong [1] to explain high temperature superconductivity. This model involves a "hopping" of Cooper pairs between layers of the unit cell which acts to amplify the pairing mechanism within the planes themselves. Recent work has shown that this model can account reasonably well for the isotope effect and the dependence of Tc on nonmagnetic in-plane impurities [2] , as well as the Knight shift curves [3] and the presence of a magnetic peak in the neutron scattering intensity [4]. In the latter case, Yin et al. emphasize that the pair tunneling must be the dominant pairing mechanism in the high-Tc cuprates in order to capture the features found in experiments. The goal of this work is to determine whether or not the ILPT model can account for the experimental observations of the magnetic field penetration depth in YBa2Cu307_a7. Calculations are performed in the weak and strong coupling limits, and the efi"ects of both small and large strengths of interlayer pair tunneling are investigated. Furthermore, as a follow up to the penetration depth calculations, both the neutron scattering intensity and the Knight shift are calculated within the ILPT formalism. The aim is to determine if the ILPT model can yield results consistent with experiments performed for these properties. The results for all three thermodynamic properties considered are not consistent with the notion that the interlayer pair tunneling must be the dominate pairing mechanism in these high-Tc cuprate superconductors. Instead, it is found that reasonable agreement with experiments is obtained for small strengths of pair tunneling, and that large pair tunneling yields results which do not resemble those of the experiments.

Mesure des champs de radiation dans le d��tecteur ATLAS et sa caverne avec les d��tecteurs au silicium �� pixels ATLAS-MPX

Les collisions proton-proton produites par le LHC imposent un environnement radiatif hostile au d��tecteur ATLAS. Afin de quantifier les effets de cet environnement sur la performance du d��tecteur et la s��curit�� du personnel, plusieurs simulations Monte Carlo ont ��t�� r��alis��es. Toutefois, la mesure directe est indispensable pour suivre les taux de radiation dans ATLAS et aussi pour v��rifier les pr��dictions des simulations. �� cette fin, seize d��tecteurs ATLAS-MPX ont ��t�� install��s �� diff��rents endroits dans les zones exp��rimentale et technique d'ATLAS. Ils sont compos��s d'un d��tecteur au silicium �� pixels appel�� MPX dont la surface active est partiellement recouverte de convertisseurs de neutrons thermiques, lents et rapides. Les d��tecteurs ATLAS-MPX mesurent en temps r��el les champs de radiation en enregistrant les traces des particules d��tect��es sous forme d'images matricielles. L'analyse des images acquises permet d'identifier les types des particules d��tect��es �� partir des formes de leurs traces. Dans ce but, un logiciel de reconnaissance de formes appel�� MAFalda a ��t�� con��u. ��tant donn�� que les traces des particules fortement ionisantes sont influenc��es par le partage de charge entre pixels adjacents, un mod��le semi-empirique d��crivant cet effet a ��t�� d��velopp��. Gr��ce �� ce mod��le, l'��nergie des particules fortement ionisantes peut ��tre estim��e �� partir de la taille de leurs traces. Les convertisseurs de neutrons qui couvrent chaque d��tecteur ATLAS-MPX forment six r��gions diff��rentes. L'efficacit�� de chaque r��gion �� d��tecter les neutrons thermiques, lents et rapides a ��t�� d��termin��e par des mesures d'��talonnage avec des sources connues. L'��tude de la r��ponse des d��tecteurs ATLAS-MPX �� la radiation produite par les collisions frontales de protons �� 7TeV dans le centre de masse a montr�� que le nombre de traces enregistr��es est proportionnel �� la luminosit�� du LHC. Ce r��sultat permet d'utiliser les d��tecteurs ATLAS-MPX comme moniteurs de luminosit��. La m��thode propos��e pour mesurer et ��talonner la luminosit�� absolue avec ces d��tecteurs est celle de van der Meer qui est bas��e sur les param��tres des faisceaux du LHC. Vu la corr��lation entre la r��ponse des d��tecteurs ATLAS-MPX et la luminosit��, les taux de radiation mesur��s sont exprim��s en termes de fluences de diff��rents types de particules par unit�� de luminosit�� int��gr��e. Un ��cart significatif a ��t�� obtenu en comparant ces fluences avec celles pr��dites par GCALOR qui est l'une des simulations Monte Carlo du d��tecteur ATLAS. Par ailleurs, les mesures effectu��es apr��s l'arr��t des collisions proton-proton ont montr�� que les d��tecteurs ATLAS-MPX permettent d'observer la d��sint��gration des isotopes radioactifs g��n��r��s au cours des collisions. L'activation r��siduelle des mat��riaux d'ATLAS peut ��tre mesur��e avec ces d��tecteurs gr��ce �� un ��talonnage en ��quivalent de dose ambiant.

Acoustic radiation and scattering from cylindrical bodies and analysis of transducer arrays

New mathematical methods to analytically investigate linear acoustic radiation and scattering from cylindrical bodies and transducer arrays are presented. Three problems of interest involving cylinders in an infinite fluid are studied. In all the three problems, the Helmholtz equation is used to model propagation through the fluid and the beam patterns of arrays of transducers are studied. In the first problem, a method is presented to determine the omni-directional and directional far-field pressures radiated by a cylindrical transducer array in an infinite rigid cylindrical baffle. The solution to the Helmholtz equation and the displacement continuity condition at the interface between the array and the surrounding water are used to determine the pressure. The displacement of the surface of each transducer is in the direction of the normal to the array and is assumed to be uniform. Expressions are derived for the pressure radiated by a sector of the array vibrating in-phase, the entire array vibrating in-phase, and a sector of the array phase-shaded to simulate radiation from a rectangular piston. It is shown that the uniform displacement required for generating a source level of 220 dB ref. ��Pa @ 1m that is omni directional in the azimuthal plane is in the order of 1 micron for typical arrays. Numerical results are presented to show that there is only a small difference between the on-axis pressures radiated by phased cylindrical arrays and planar arrays. The problem is of interest because cylindrical arrays of projectors are often used to search for underwater objects. In the second problem, the errors, when using data-independent, classical, energy and split beam correlation methods, in finding the direction of arrival (DOA) of a plane acoustic wave, caused by the presence of a solid circular elastic cylindrical stiffener near a linear array of hydrophones, are investigated. Scattering from the effectively infinite cylinder is modeled using the exact axisymmetric equations of motion and the total pressures at the hydrophone locations are computed. The effect of the radius of the cylinder, a, the distance between the cylinder and the array, b, the number of hydrophones in the array, 2H, and the angle of incidence of the wave, ��, on the error in finding the DOA are illustrated using numerical results. For an array that is about 30 times the wavelength and for small angles of incidence (��<10), the error in finding the DOA using the energy method is less than that using the split beam correlation method with beam steered to ��; and in some cases, the error increases when b increases; and the errors in finding the DOA using the energy method and the split beam correlation method with beam steered to �� vary approximately as a7 / 4 . The problem is of interest because elastic stiffeners ��� in nearly acoustically transparent sonar domes that are used to protect arrays of transducers ��� scatter waves that are incident on it and cause an error in the estimated direction of arrival of the wave. In the third problem, a high-frequency ray-acoustics method is presented and used to determine the interior pressure field when a plane wave is normally incident on a fluid cylinder embedded in another infinite fluid. The pressure field is determined by using geometrical and physical acoustics. The interior pressure is expressed as the sum of the pressures due to all rays that pass through a point. Numerical results are presented for ka = 20 to 100 where k is the acoustic wavenumber of the exterior fluid and a is the radius of the cylinder. The results are in good agreement with those obtained using field theory. The directional responses, to the plane wave, of sectors of a circular array of uniformly distributed hydrophones in the embedded cylinder are then computed. The sectors are used to simulate linear arrays with uniformly distributed normals by using delays. The directional responses are compared with the output from an array in an infinite homogenous fluid. These outputs are of interest as they are used to determine the direction of arrival of the plane wave. Numerical results are presented for a circular array with 32 hydrophones and 12 hydrophones in each sector. The problem is of interest because arrays of hydrophones are housed inside sonar domes and acoustic plane waves from distant sources are scattered by the dome filled with fresh water and cause deterioration in the performance of the array.

Investigations on the radiation characteristics of new hollow dielectric horn antennas

Investigations on the design and development of certain new hollow dielectric hom antennas of rectangular cross section have been carried out. The main shortcoming of the existing ordinary hollow dielectric hom antenna (HDH) is the abrupt discontinuity at the feed-end. A new launching technique using a dielectric rod is introduced to overcome this limitation. Also a strip loading technique is employed for further modification of the antenna. Radiation parameters of new I-IDH antennas of Eplane sectoral, H-plane sectoral and pyramidal types were studied and are found to be very attractive. Theoretical approach based on Marcatili���s principle and two aperture theory along with diffraction theory and image theory is used to support the experimental findings. The HDH is considered as solid horn of effective dielectric constant and the aperture field is evaluated. The antenna is excited by the open waveguide in the dominant TE1o mode and so the existence of any hybrid mode is mled-out. The theoretical results are observed to be in good agreement with the experimental results.

THz Plasma Waves in Field-Effect-Transistors: A Monte Carlo Study

Sensing with electromagnetic waves having frequencies in the Terahertz-range is a very attractive investigative method with applications in fundamental research and industrial settings. Up to now, a lot of sources and detectors are available. However, most of these systems are bulky and have to be used in controllable environments such as laboratories. In 1993 Dyakonov and Shur suggested that plasma waves developing in field-effect-transistors can be used to emit and detect THz-radiation. Later on, it was shown that these plasma waves lead to rectification and allows for building efficient detectors. In contrast to the prediction that these plasma waves lead to new promising solid-state sources, only a few weak sources are known up to now. This work studies THz plasma waves in semiconductor devices using the Monte Carlo method in order to resolve this issue. A fast Monte Carlo solver was developed implementing a nonparabolic bandstructure representation of the used semiconductors. By investigating simplified field-effect-transistors it was found that the plasma frequency follows under equilibrium conditions the analytical predictions. However, no current oscillations were found at room temperature or with a current flowing in the channel. For more complex structures, consisting of ungated and gated regions, it was found that the plasma frequency does not follow the value predicted by the dispersion relation of the gated nor the ungated device.

A "Trojan horse" strategy to reverse drug-resistance in brain tumors

Los gliomas malignos representan una de las formas m��s agresivas de los tumores del sistema nervioso central (SNC). De acuerdo con la clasificaci��n de los tumores cerebrales de la Organizaci��n Mundial de la Salud (OMS), los astrocitomas han sido categorizados en cuatro grados, determinados por la patolog��a subyacente. Es as�� como los gliomas malignos (o de alto grado) incluyen el glioma anapl��sico (grado III) as�� como el glioblastoma multiforme (GBM, grado IV),estos ��ltimos los m��s agresivos con el peor pron��stico (1). El manejo terap��utico de los tumores del SNC se basa en la cirug��a, la radioterapia y la quimioterapia, dependiendo de las caracter��sticas del tumor, el estadio cl��nico y la edad (2),(3), sin embargo ninguno de los tratamientos est��ndar es completamente seguro y compatible con una calidad de vida aceptable (3), (4). En general, la quimioterapia es la primera opci��n en los tumores diseminados, como el glioblastoma invasivo y el meduloblastoma de alto riesgo o con met��stasis m��ltiple, pero el pron��stico en estos pacientes es muy pobre (2),(3). Solamente nuevas terapias dirigidas (2) como las terapias anti-angiog��nicas (4); o terapias g��nicas muestran un beneficio real en grupos limitados de pacientes con defectos moleculares espec��ficos conocidos (4). De este modo, se hace necesario el desarrollo de nuevas terapias farmacol��gicas para atacar los tumores cerebrales. Frente a las terapias los gliomas malignos son con frecuencia quimioresistentes, y esta resistencia parece depender de al menos dos mecanismos: en primer lugar, la pobre penetraci��n de muchas drogas antic��ncer a trav��s de la barrera hematoencef��lica (BBB: Blood Brain Barrier), la barrera del fluido sangre-cerebroespinal (BCSFB: Blood-cerebrospinal fluid barrier) y la barrera sangre-tumor (BTB: blood-tumor barrier). Dicha resistencia se debe a la interacci��n de la droga con varios transportadores o bombas de eflujo de droga ABC (ABC: ATP-binding cassette) que se sobre expresan en las c��lulas endoteliales o epiteliales de estas barreras. En segundo lugar, estos transportadores de eflujo de drogas ABC propios de las c��lulas tumorales confieren un fenotipo conocido como resistencia a multidrogas (MDR: multidrug resistance), el cual es caracter��stico de varios tumores s��lidos. Este fenotipo tambi��n est�� presente en los tumores del SNC y su papel en gliomas es objeto de investigaci��n (5). Por consiguiente el suministro de medicamentos a trav��s de la BBB es uno de los problemas vitales en los tratamientos de terapia dirigida. Estudios recientes han demostrado que algunas mol��culas peque��as utilizadas en estas terapias son sustratos de la glicoprote��na P (Pgp: P-gycoprotein), as�� como tambi��n de otras bombas de eflujo como las prote��nas relacionadas con la resistencia a multidrogas (MRPs: multidrug resistance-related proteins (MRPs) o la prote��na relacionada con c��ncer de seno (BCRP: breast-cancer resistance related protein)) que no permiten que las drogas de este tipo alcancen el tumor (1). Un sustrato de Pgp y BCRP es la DOXOrubicina (DOXO), un f��rmaco utilizado en la terapia anti c��ncer, el cual es muy eficaz para atacar las c��lulas del tumor cerebral in vitro, pero con un uso cl��nico limitado por la poca entrega a trav��s de la barrera hematoencef��lica (BBB) y por la resistencia propia de los tumores. Por otra parte las c��lulas de BBB y las c��lulas del tumor cerebral tienen tambi��n prote��nas superficiales, como el receptor de la lipoprote��na de baja densidad (LDLR), que podr��a utilizarse como blanco terap��utico en BBB y tumores cerebrales. Es asi como la importancia de este estudio se basa en la generaci��n de estrategias terap��uticas que promuevan el paso de las drogas a trav��s de la barrera hematoencefalica y tumoral, y a su vez, se reconozcan mecanismos celulares que induzcan el incremento en la expresi��n de los transportadores ABC, de manera que puedan ser utilizados como blancos terap��uticos.Este estudio demostr�� que el uso de una nueva estrategia basada en el ���Caballo de Troya���, donde se combina la droga DOXOrubicina, la cual es introducida dentro de un liposoma, salvaguarda la droga de manera que se evita su reconocimiento por parte de los transportadores ABC tanto de la BBB como de las c��lulas del tumor. La construcci��n del liposoma permiti�� utilizar el receptor LDLR de las c��lulas asegurando la entrada a trav��s de la BBB y hacia las c��lulas tumorales a trav��s de un proceso de endocitosis. Este mecanismo fue asociado al uso de estatinas o drogas anticolesterol las cuales favorecieron la expresi��n de LDLR y disminuyeron la actividad de los transportadores ABC por nitraci��n de los mismos, incrementando la eficiencia de nuestro Caballo de Troya. Por consiguiente demostramos que el uso de una nueva estrategia o formulaci��n denominada ApolipoDOXO m��s el uso de estatinas favorece la administraci��n de f��rmacos a trav��s de la BBB, venciendo la resistencia del tumor y reduciendo los efectos colaterales dosis dependiente de la DOXOrubicina. Adem��s esta estrategia del "Caballo de Troya", es un nuevo enfoque terap��utico que puede ser considerado como una nueva estrategia para aumentar la eficacia de diferentes f��rmacos en varios tumores cerebrales y garantiza una alta eficiencia incluso en un medio hip��xico,caracter��stico de las c��lulas cancerosas, donde la expresi��n del transportador Pgp se vi�� aumentada. Teniendo en cuenta la relaci��n entre algunas v��as de se��alizaci��n reconocidas como moduladores de la actividad de Pgp, este estudio presenta no solo la estrategia del Caballo de Troya, sino tambi��n otra propuesta terap��utica relacionada con el uso de Temozolomide m��s DOXOrubicina. Esta estrategia demostr�� que el temozolomide logra penetrar la BBB por que interviene en la via de se��alizaci��n de la Wnt/GSK3/��-catenina, la cual modula la expresi��n del transportador Pgp. Se demostr�� que el TMZ disminuye la prote��na y el mRNA de Wnt3 permitiendo plantear la hip��tesis de que la droga al disminuir la transcripci��n del gen Wnt3 en c��lulas de BBB, incrementa la activaci��n de la v��a fosforilando la ��-catenina y conduciendo a disminuir la ��-catenina nuclear y por tanto su uni��n al promotor del gen mdr1. Con base en los resultados este estudio permiti�� el reconocimiento de tres mecanismos b��sicos relacionados con la expresi��n de los transportadores ABC y asociados a las estrategias empleadas: el primero fue el uso de las estatinas, el cual condujo a la nitraci��n de los transportadores disminuyendo su actividad por la via del factor de transcripci��n NF��B; el segundo a partir del uso del temozolomide, el cual metila el gen de Wnt3 reduciendo la actividad de la via de se��alizaci��n de la la ��-catenina, disminuyendo la expresi��n del transportador Pgp. El tercero consisti�� en la determinaci��n de la relaci��n entre el eje RhoA/RhoA quinasa como un modulador de la via (no can��nica) GSK3/��-catenina. Se demostr�� que la prote��na quinasa RhoA promovi�� la activaci��n de la prote��na PTB1, la cual al fosforilar a GSK3 indujo la fosforilaci��n de la ��-catenina, lo cual dio lugar a su destrucci��n por el proteosoma, evitando su uni��n al promotor del gen mdr1 y por tanto reduciendo su expresi��n. En conclusi��n las estrategias propuestas en este trabajo incrementaron la citotoxicidad de las c��lulas tumorales al aumentar la permeabilidad no solo de la barrera hematoencef��lica, sino tambi��n de la propia barrera tumoral. Igualmente, la estrategia del ���Caballo de Troya��� podr��a ser ��til para la terapia de otras enfermedades asociadas al sistema nervioso central. Por otra parte estos estudios indican que el reconocimiento de mecanismos asociados a la expresi��n de los transportadores ABC podr��a constituir una herramienta clave en el desarrollo de nuevas terapias antic��ncer.

Estimating surface net solar radiation by use of Landsat-5 TM and digital elevation models

The ground surface net solar radiation is the energy that drives physical and chemical processes at the ground surface. In this paper, multi-spectral data from the Landsat-5 TM, topographic data from a gridded digital elevation model, field measurements, and the atmosphere model LOWTRAN 7 are used to estimate surface net solar radiation over the FIFE site. Firstly an improved method is presented and used for calculating total surface incoming radiation. Then, surface albedo is integrated from surface reflectance factors derived from remotely sensed data from Landsat-5 TM. Finally, surface net solar radiation is calculated by subtracting surface upwelling radiation from the total surface incoming radiation.

Two methods for modelling the propagation of terahertz radiation in a layered structure

Modelling the interaction of terahertz(THz) radiation with biological tissueposes many interesting problems. THzradiation is neither obviously described byan electric field distribution or anensemble of photons and biological tissueis an inhomogeneous medium with anelectronic permittivity that is bothspatially and frequency dependent making ita complex system to model.A three-layer system of parallel-sidedslabs has been used as the system throughwhich the passage of THz radiation has beensimulated. Two modelling approaches havebeen developed a thin film matrix model anda Monte Carlo model. The source data foreach of these methods, taken at the sametime as the data recorded to experimentallyverify them, was a THz spectrum that hadpassed though air only.Experimental verification of these twomodels was carried out using athree-layered in vitro phantom. Simulatedtransmission spectrum data was compared toexperimental transmission spectrum datafirst to determine and then to compare theaccuracy of the two methods. Goodagreement was found, with typical resultshaving a correlation coefficient of 0.90for the thin film matrix model and 0.78 forthe Monte Carlo model over the full THzspectrum. Further work is underway toimprove the models above 1 THz.

Preliminary results on the non-thermal effects of 200-350 GHz radiation on the growth rate of S. cerevisiae cells in microcolonies

We report preliminary results from studies of biological effects induced by non-thermal levels of non-ionizing electromagnetic radiation. Exponentially growing Saccharomyces cerevisiae yeast cells grown on dry media were exposed to electromagnetic fields in the 200���350 GHz frequency range at low power density to observe possible non-thermal effects on the microcolony growth. Exposure to the electromagnetic field was conducted over 2.5 h. The data from exposure and control experiments were grouped into either large-, medium- or small-sized microcolonies to assist in the accurate assessment of growth. The three groups showed significant differences in growth between exposed and control microcolonies. A statistically significant enhanced growth rate was observed at 341 GHz. Growth rate was assessed every 30 min via time-lapse photography. Possible interaction mechanisms are discussed, taking into account Frohlich's hypothesis.

Extracting quantitative structural parameters for disordered polymers from neutron scattering data

The organization of non-crystalline polymeric materials at a local level, namely on a spatial scale between a few and 100 a, is still unclear in many respects. The determination of the local structure in terms of the configuration and conformation of the polymer chain and of the packing characteristics of the chain in the bulk material represents a challenging problem. Data from wide-angle diffraction experiments are very difficult to interpret due to the very large amount of information that they carry, that is the large number of correlations present in the diffraction patterns.We describe new approaches that permit a detailed analysis of the complex neutron diffraction patterns characterizing polymer melts and glasses. The coupling of different computer modelling strategies with neutron scattering data over a wide Q range allows the extraction of detailed quantitative information on the structural arrangements of the materials of interest. Proceeding from modelling routes as diverse as force field calculations, single-chain modelling and reverse Monte Carlo, we show the successes and pitfalls of each approach in describing model systems, which illustrate the need to attack the data analysis problem simultaneously from several fronts.

Extracting and validating force fields for disordered polymeric materials from neutron scattering data

We present a new approach that allows the determination and refinement of force field parameters for the description of disordered macromolecular systems from experimental neutron diffraction data obtained over a large Q range. The procedure is based on tight coupling between experimentally derived structure factors and computer modelling. By separating the potential into terms representing respectively bond stretching, angle bending and torsional rotation and by treating each of them separately, the various potential parameters are extracted directly from experiment. The procedure is illustrated on molten polytetrafluoroethylene.

Extracting force fields for disordered polymeric materials from neutron scattering data

We present a new approach that allows the determination of force-field parameters for the description of disordered macromolecular systems from experimental neutron diffraction data obtained over a large Q range. The procedure is based on a tight coupling between experimentally derived structure factors and computer modelling. We separate the molecular potential into non-interacting terms representing respectively bond stretching, angle bending and torsional rotation. The parameters for each of the potentials are extracted directly from experimental data through comparison of the experimental structure factor and those derived from atomistic level molecular models. The viability of these force fields is assessed by comparison of predicted large-scale features such as the characteristic ratio. The procedure is illustrated on molten poly(ethylene) and poly(tetrafluoroethylene).

A variational method to retrieve the extinction profile in liquid clouds using multiple field-of-view lidar

Liquid clouds play a profound role in the global radiation budget but it is difficult to remotely retrieve their vertical profile. Ordinary narrow field-of-view (FOV) lidars receive a strong return from such clouds but the information is limited to the first few optical depths. Wideangle multiple-FOV lidars can isolate radiation scattered multiple times before returning to the instrument, often penetrating much deeper into the cloud than the singly-scattered signal. These returns potentially contain information on the vertical profile of extinction coefficient, but are challenging to interpret due to the lack of a fast radiative transfer model for simulating them. This paper describes a variational algorithm that incorporates a fast forward model based on the time-dependent two-stream approximation, and its adjoint. Application of the algorithm to simulated data from a hypothetical airborne three-FOV lidar with a maximum footprint width of 600m suggests that this approach should be able to retrieve the extinction structure down to an optical depth of around 6, and total opticaldepth up to at least 35, depending on the maximum lidar FOV. The convergence behavior of Gauss-Newton and quasi-Newton optimization schemes are compared. We then present results from an application of the algorithm to observations of stratocumulus by the 8-FOV airborne ���THOR��� lidar. It is demonstrated how the averaging kernel can be used to diagnose the effective vertical resolution of the retrieved profile, and therefore the depth to which information on the vertical structure can be recovered. This work enables exploitation of returns from spaceborne lidar and radar subject to multiple scattering more rigorously than previously possible.