Intrusion of Warm Surface Water Beneath the McMurdo Ice Shelf, Antarctica

A 6 month temperature record collected below McMurdo Ice Shelf in 2011-2012 shows the temporal and spatial structure of the summertime warm water signal that penetrates beneath the ice shelf. The strength and duration of the warm water intrusion suggest an annual melt rate at Windless Bight of 0.71 m/yr. A Ross Sea numerical model demonstrates a seasonal warm water pathway leading from the west side of the Ross Sea Polynya (RSP) toward McMurdo Sound. The warm water enters McMurdo Sound, subducts beneath the ice shelf and causes accelerated summer melting. Temperature data were recorded using Distributed Temperature Sensing fiber optics, which gives a vertical temperature profile at a 1 m vertical resolution. This study constitutes one of the first successful implementations of this technology in Polar Regions

SCHEME FOR GENERATING AND TRANSPORTING THZ RADIATION TO THE X-RAY EXPERIMENTAL HALL AT THE EUROPEAN XFEL

Abstract We consider generation of THz radiation from the spent electron beam downstream of the SASE2 undulator in the electron beam dump area. The THz output must propagate at least for 250 meters through the photon beam tunnel to the experimental hall to reach the SASE2 X-ray hutches. We propose to use an open beam waveguide such as an iris guide as transmission line. In order to efficiently couple radiation into the iris transmission line, generation of the THz radiation pulse can be performed directly within the iris guide. The line transporting the THz radiation to the SASE2 X-ray hutches introduces a path delay of about 20 m. Since THz pump/X-ray probe experiments should be enabled, we propose to exploit the European XFEL baseline multi-bunch mode of operation, with 222 ns electron bunch separation, in order to cope with the delay between THz and X-ray pulses. We present start-to-end simulations for 1 nC bunch operation-parameters, optimized for THz pump/X-ray probe experiments. Detailed characterization of the THz and SASE X-ray radiation pulses is performed. Highly focused THz beams will approach the high field limit of 1 V/atomic size

Ethnic differences in the association of fat and lean mass with bone mineral density in the Singapore population

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Exposure-age record of Holocene ice sheet and ice shelf change in the northeast Antarctic Peninsula

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New Measure of Insulin Sensitivity Predicts Cardiovascular Disease Better than HOMA Estimated Insulin Resistance

10.1371/journal.pone.0074410PLoS ONE89-POLN

The ice-free topography of Svalbard

We present a first version of the Svalbard ice-free topography (SVIFT1.0) using a mass-conserving approach for mapping glacier ice thickness. SVIFT1.0 is informed by more than 900’000 point-measurements of glacier thickness, totalling almost 8’300 km of thickness profiles. It is publicly available for download. Our estimate for the total ice volume is 6’253km3, equivalent to 1.6cm sea-level rise. The thickness map suggests that 13% of the glacierised area is grounded below sea-level. Thickness values are provided together with a map of error estimates that comprise uncertainties in the thickness surveys as well as in other input variables. Aggregated error estimates are used to define a likely ice-volume range of 5’200-7’400km3. The ice-front thickness of marine-terminating glaciers is a key quantity for ice-loss attribution because it controls the potential ice discharge by iceberg calving into the ocean. We find a mean ice-front thickness of 133m for the archipelago

Evaluation of time domain electromagnetic fields radiated by constant velocity moving particles traveling along an arbitrarily shaped cross-section waveguide using frequency domain Green's functions

A technique for the accurate computation of the time domain electromagnetic fields radiated by a charged distribution traveling along an arbitrarily shaped waveguide region is presented. Based on the transformation (by means of the standard Fourier analysis) of the time-varying current density of the analyzed problem to the frequency domain, the resulting equivalent current is further convolved with the dyadic electric and magnetic Green's functions. Moreover, we show that only the evaluation of the transverse magnetic modes of the structure is required for the calculation of fields radiated by particles traveling in the axial direction. Finally, frequency domain electric and magnetic fields are transformed back to the time domain, just obtaining the total fields radiated by the charged distribution. Furthermore, we present a method for the computation of the wakefields of arbitrary cross-section uniform waveguides from the resulting field expressions. Several examples of charged particles moving in the axial direction of such waveguides are included.The authors would like to thank ESA/ESTEC for having cofunded this research activity through the Network Partnering Initiative program and through the project "Multipactor Analysis in Planar Transmission Lines" (contract 20841/08/NL/GLC). We also are grateful to the Spanish government and the local Council of Murcia for their support through the projects CICYT Ref. TEC2010-21520-C04-04 and SENECA Ref. 08833/PI/08, respectively.Jimenez Nogales, M.; Marini, S.; Gimeno Martinez, B.; Alvarez Melcon, A.; Quesada Pereira, FD.; Boria Esbert, VE.; Soto Pacheco, P.... (2012). Evaluation of time domain electromagnetic fields radiated by constant velocity moving particles traveling along an arbitrarily shaped cross-section waveguide using frequency domain Green's functions. Radio Science. 47(5):1-14. https://doi.org/10.1029/2012RS005008S114475Alvarez-Melcon, A., & Mosig, J. R. (2000). Two techniques for the efficient numerical calculation of the Green’s functions for planar shielded circuits and antennas. IEEE Transactions on Microwave Theory and Techniques, 48(9), 1492-1504. doi:10.1109/22.869000Bane, K. L. F., Wilson, P. B., & Weiland, T. (1985). Wake fields and wake field acceleration. AIP Conference Proceedings. doi:10.1063/1.35182Bozzi, M., Perregrini, L., Alvarez Melcon, A., Guglielmi, M., & Conciauro, G. (2001). MoM/BI-RME analysis of boxed MMICs with arbitrarily shaped metallizations. IEEE Transactions on Microwave Theory and Techniques, 49(12), 2227-2234. doi:10.1109/22.971604Burov, A., & Danilov, V. (1999). Suppression of Transverse Bunch Instabilities by Asymmetries in the Chamber Geometry. Physical Review Letters, 82(11), 2286-2289. doi:10.1103/physrevlett.82.2286Cogollos, S., Marini, S., Boria, V. E., Soto, P., Vidal, A., Esteban, H., … Gimeno, B. (2003). Efficient modal analysis of arbitrarily shaped waveguides composed of linear, circular, and elliptical arcs using the BI-RME method. IEEE Transactions on Microwave Theory and Techniques, 51(12), 2378-2390. doi:10.1109/tmtt.2003.819776Conciauro, G., Bressan, M., & Zuffada, C. (1984). Waveguide Modes Via an Integral Equation Leading to a Linear Matrix Eigenvalue Problem. IEEE Transactions on Microwave Theory and Techniques, 32(11), 1495-1504. doi:10.1109/tmtt.1984.1132880Deshpande , M. D. 1997 Analysis of discontinuities in a rectangular waveguide using dyadic Green's function approach in conjuntion with Method of Moments Langley Res. Cent., NASA Hampton, Va.Felsen, L. B., & Marcuvitz, N. (1994). Radiation and Scattering of Waves. doi:10.1109/9780470546307Figueroa, H., Gai, W., Konecny, R., Norem, J., Ruggiero, A., Schoessow, P., & Simpson, J. (1988). Direct Measurement of Beam-Induced Fields in Accelerating Structures. Physical Review Letters, 60(21), 2144-2147. doi:10.1103/physrevlett.60.2144Gai, W., Kanareykin, A. D., Kustov, A. L., & Simpson, J. (1997). Numerical simulations of intense charged-particle beam propagation in a dielectric wake-field accelerator. Physical Review E, 55(3), 3481-3488. doi:10.1103/physreve.55.3481Gluckstern, R. L., van Zeijts, J., & Zotter, B. (1993). Coupling impedance of beam pipes of general cross section. Physical Review E, 47(1), 656-663. doi:10.1103/physreve.47.656Hanson, G. W., & Yakovlev, A. B. (2002). Operator Theory for Electromagnetics. doi:10.1007/978-1-4757-3679-3Hess, M., Park, C. S., & Bolton, D. (2007). Green’s function based space-charge field solver for electron source simulations. Physical Review Special Topics - Accelerators and Beams, 10(5). doi:10.1103/physrevstab.10.054201Iriso-Ariz, U., Caspers, F., & Mostacci, A. (s. f.). Evaluation of the horizontal to vertical transverse impedance ratio for LHC beam screen using a 2D electrostatic code. Proceedings of the 2003 Bipolar/BiCMOS Circuits and Technology Meeting (IEEE Cat. No.03CH37440). doi:10.1109/pac.2003.1289954Jing, C., Liu, W., Xiao, L., Gai, W., Schoessow, P., & Wong, T. (2003). Dipole-mode wakefields in dielectric-loaded rectangular waveguide accelerating structures. Physical Review E, 68(1). doi:10.1103/physreve.68.016502Kim, S. H., Chen, K. W., & Yang, J. S. (1990). Modal analysis of wake fields and its application to elliptical pill‐box cavity with finite aperture. Journal of Applied Physics, 68(10), 4942-4951. doi:10.1063/1.347079Lutman, A., Vescovo, R., & Craievich, P. (2008). Electromagnetic field and short-range wake function in a beam pipe of elliptical cross section. Physical Review Special Topics - Accelerators and Beams, 11(7). doi:10.1103/physrevstab.11.074401Ng, K.-Y. (1990). Wake fields in a dielectric-lined waveguide. Physical Review D, 42(5), 1819-1828. doi:10.1103/physrevd.42.1819Palumbo, L., Vaccaro, V. G., & Wustefeld, G. (1984). Coupling Impedance in a Circular Particle Accelerator, a Particular Case: Circular Beam, Elliptic Chamber. IEEE Transactions on Nuclear Science, 31(4), 1011-1020. doi:10.1109/tns.1984.4333427Panofsky, W. K. H., & Wenzel, W. A. (1956). Some Considerations Concerning the Transverse Deflection of Charged Particles in Radio‐Frequency Fields. Review of Scientific Instruments, 27(11), 967-967. doi:10.1063/1.1715427Rahmat-Samii, Y. (1975). On the Question of Computation of the Dyadic Green’s Function at the Source Region in Waveguides and Cavities (Short Papers). IEEE Transactions on Microwave Theory and Techniques, 23(9), 762-765. doi:10.1109/tmtt.1975.1128671Rosing, M., & Gai, W. (1990). Longitudinal- and transverse-wake-field effects in dielectric structures. Physical Review D, 42(5), 1829-1834. doi:10.1103/physrevd.42.1829Rumolo, G., Ruggiero, F., & Zimmermann, F. (2001). Simulation of the electron-cloud build up and its consequences on heat load, beam stability, and diagnostics. Physical Review Special Topics - Accelerators and Beams, 4(1). doi:10.1103/physrevstab.4.012801Salah, W. (2004). Analytical and numerical investigations of the evolution of wake fields of accelerated electron beams encountering cavity discontinuities in laser-driven RF-free electron laser photoinjector. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 533(3), 248-257. doi:10.1016/j.nima.2004.05.129Salah, W., & Dolique, J.-M. (1999). Wake field of electron beam accelerated in a RF-gun of free electron laser «ELSA». Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 431(1-2), 27-37. doi:10.1016/s0168-9002(99)00255-7Stupakov, G., Bane, K. L. F., & Zagorodnov, I. (2007). Optical approximation in the theory of geometric impedance. Physical Review Special Topics - Accelerators and Beams, 10(5). doi:10.1103/physrevstab.10.054401Wang, J. 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Drilling of glacier boreholes with a hydrophilic liquid

During the last twenty years over 10000m of ice core have been recovered through the use of antifreeze thermal electric drills (ATED). An environmentally safe ethanol-water solution (EWS) was utilized as a borehole liquid. The ATED method has been widely used on high mountain temperate and polar glaciers. At glacier temperatures (T_i) from -28 to -8℃ the ATED penetration rate is about 420-450m/wk (I. A. ZOTIKOV; CRREL Rep., 79-24,12p., 1979; V. S. ZAGORODNOV; Ice Core Drilling : Proc. 3rd Int. Workshop Ice Drilling Tech., 97,1989). In Antarctica a borehole of 800m depth was drilled in ice at T_i=-53℃ in two month. Drilling of this borehole was continued the next field season. The major cause of ice core fracture under thermal drilling is thermoelastic stresses. The quality of an ice core taken under ATED can be significantly improved applying the forced circulation of EWS at the borehole kerf. Experimental and theoretical studies demonstrate that a modified ATED (m-ATED) reduces power consumption by 20%-40%. The penetration rate of the m-ATED at low temperatures (below -30℃) is estimated to be about 450m/wk. The logistic cost for deep (>1000m) drilling with ATED is estimated to be about 25% of the conventional thermal or mechanical drilling. Laboratory experiments show that ice can be dissolved by EWS. The phenomenon of ice dissolution by EWS can underlie the dissolution drilling technology (DDT). Further development of DDT technology may offer : simple drill structure, low power consumption, low thermal effect on ice core and borehole wall, ability to penetrate dirty ice, and low logistic cost