Observation of a cascaded process in intracavity terahertz optical parametric oscillators based on lithium niobate

Cascaded difference frequency generation has been observed in intracavity optical parametric oscillators based on bulk lithium niobate and producing nanosecond pulses of terahertz radiation. Two idler waves are generated, namely: the primary idler wave associated with the parametric down conversion process itself; and a secondary idler wave, due to difference frequency generation. Experimental investigations of the frequency, temporal evolution, propagation direction, intensity, phase matching and oscillation threshold of the generated down-converted waves are reported. The overall generation efficiency for the terahertz radiation is enhanced, thereby overcoming the Manley-Rowe limit. Advantages of the present approach over schemes based on periodically poled lithium niobate are identified.Publisher PDFPeer reviewe

Laser Doppler velocimeter system simulation for sensing aircraft wake vortices. Part 2: Processing and analysis of LDV data (for runs 1023 and 2023)

A data analysis program constructed to assess LDV system performance, to validate the simulation model, and to test various vortex location algorithms is presented. Real or simulated Doppler spectra versus range and elevation is used and the spatial distributions of various spectral moments or other spectral characteristics are calculated and displayed. Each of the real or simulated scans can be processed by one of three different procedures: simple frequency or wavenumber filtering, matched filtering, and deconvolution filtering. The final output is displayed as contour plots in an x-y coordinate system, as well as in the form of vortex tracks deduced from the maxima of the processed data. A detailed analysis of run number 1023 and run number 2023 is presented to demonstrate the data analysis procedure. Vortex tracks and system range resolutions are compared with theoretical predictions

A feasibility study for the detection of upper atmospheric winds using a ground based laser Doppler velocimeter

A possible measurement program designed to obtain the information requisite to determining the feasibility of airborne and/or satellite-borne LDV (Laser Doppler Velocimeter) systems is discussed. Measurements made from the ground are favored over an airborne measurement as far as for the purpose of determining feasibility is concerned. The expected signal strengths for scattering at various altitude and elevation angles are examined; it appears that both molecular absorption and ambient turbulence degrade the signal at low elevation angles and effectively constrain the ground based measurement of elevation angles exceeding a critical value. The nature of the wind shear and turbulence to be expected are treated from a linear hydrodynamic model - a mountain lee wave model. The spatial and temporal correlation distances establish requirements on the range resolution, the maximum detectable range and the allowable integration time

Laser Doppler velocimeter system simulation for sensing aircraft wake vortices

A hydrodynamic model of aircraft vortex wakes in an irregular wind shear field near the ground is developed and used as a basis for modeling the characteristics of a laser Doppler detection and vortex location system. The trailing vortex sheet and the wind shear are represented by discrete free vortices distributed over a two-dimensional grid. The time dependent hydrodynamic equations are solved by direct numerical integration in the Boussinesq approximation. The ground boundary is simulated by images, and fast Fourier Transform techniques are used to evaluate the vorticity stream function. The atmospheric turbulence was simulated by constructing specific realizations at time equal to zero, assuming that Kolmogoroff's law applies, and that the dissipation rate is constant throughout the flow field. The response of a simulated laser Doppler velocimeter is analyzed by simulating the signal return from the flow field as sensed by a simulation of the optical/electronic system

Exercise rehabilitation for recovery from critical illness (Protocol)

Queen Margaret University, Edinburgh, UK. As part of an ongoing research education programme.This is the protocol for a review and there is no abstract. The objectives are as follows: The objective of this systematic review is to assess the effectiveness of exercise rehabilitation programmes, initiated after ICU discharge, on improving functional exercise capacity and quality of life in adult ICU survivors who have been mechanically ventilated for more than 24 hours. We will compare an exercise intervention to any other intervention or a control or 'usual care' programme. Exercise includes any structured or taught programmes. Respiratory or inspiratory muscle training is excluded due to it being initiated within the ICU environment, for example with weaning from a ventilator, and not as post-discharge rehabilitation as required for this review.sch_phyAngus 1997 Angus, DC. Understanding the incidence and long-term outcomes of ARDS. In: Gullo, A editor(s). Anaesthesia, pain, intensive care and emergency medicine: a scientific report. Berlin Heidelberg New York: Springer, 1997:289-98. Angus 2003 Angus DC, Carlet J, Brussels Roundtable 2002 Participants. Surviving intensive care: a report from the 2002 Brussels Roundtable. Intensive Care Medicine 2003;29(3):368-77. [PUBMED: 12536269 ] Baumgartner 1999 Baumgartner WA,Walinsky PL, Salazar JD, Tseng EE, Brock MV, Doty JR, et al.Assessing the impact of cerebral injury after cardiac surgery: will determining the mechanism reduce the injury?. The Annals of Thoracic Surgery 1999;67(6):1871-3. [PUBMED: 10391329] Brown 1990 Brown AB, McCartney N, Sale DG. Positive adaptation to weightlifting in the elderly. Journal of Applied Physiology 1990;69(5): 1725-33. [PUBMED: 2272965] Burtin 2009 Burtin C, Clerckx B, Robbeets C, Ferdinande P, Langer D, Troosters T, et al.Early exercise in critically ill patients enhances short-term functional recovery. Critical Care Medicine 2009;37(9): 2499-505. [PUBMED: 19623052] Chaboyer 2003 Chaboyer W, Grace J. Following the path of ICU survivors: a quality improvement activity. Nursing in Critical Care 2003;8(4): 149-55. [PUBMED: 12940690] Eddleston 2000 Eddleston J, White P, Guthrie E. Survival, morbidity, and quality of life after discharge from intensive care. Critical Care Medicine 2000; 28(7):2293-9. [PUBMED: 10921555] Elliott 2006 Elliott D, McKinley S, Alison J, Aitken L, King M. Study protocol: Home-based rehabilitation for survivors of a critical illness. Critical Care 2006;10(3):R90. [PUBMED: 16792792 ] Fiatarone 1994 Fiatarone MA, O'Neill EF, Ryan ND, Clements KM, Solares GR, Nelson ME, et al.Exercise training and nutritional supplementation for physical frailty in very elderly people. New England Journal of Medicine 1994;330(25):1769-75. [PUBMED: 8190152] Fletcher 2003 Fletcher S, Kennedy D, Ghosh I, Misra V, Kiff K, et al.Persistant neuromuscular and neurophysiological abnormalities in long-term survivors of prolonged critical illness. Critical Care Medicine 2003; 31(4):1012-6. [PUBMED: 12682465] Frank 2000 Frank M, Schlapfer H, Otte B, Yasikoff N, Conzelmann M. Results of neurorehabilitation. An outcome study 20 months after stroke. Praxis 2000;89(44):1799-808. [PUBMED: 11109917] Gill 2002 Gill TM, Baker DI, Gottschalk M, Peduzzi PN, Allore H, Byers A. A program to prevent functional decline in physically frail, elderly persons who live at home. New England Journal of Medicine 2002; 347(14):1068-74. [PUBMED: 12362007] Grimby 1986 Grimby G. Physical activity and muscle training in the elderly. Acta Medica Scandinavica. Supplementum. 1986;711:233-7. [PUBMED: 3535411] Guyatt 2008 Guyatt GH, Oxman AD, Kunz R, Vist GE, Falck-Ytter Y, Schunemann HJ, et al.What is quality of evidence- and why is it important to clinicians?. BMJ 2008;336:995-8. [PUBMED: 18456631] Higgins 2008 Higgins JPT, Green S, editors. Cochrane Handbook for Systematic Reviews of Interventions Version 5.0.1 [updated September 2008]. Available from www.cochrane-handbook.org: The Cochrane Collaboration, 2008. Iversen 2003 Iversen MD, Fossel AH, Katz JN. Enhancing function in older adults with chronic low back pain: a pilot study of endurance training. Archives of Physical Medicine and Rehabilitation 2003;84 (9):1324-31. [PUBMED: 13680569] Jolliffe 2001 Jolliffe J, Rees K, Taylor RRS, Thompson DR, Oldridge N, Ebrahim S. Exercise-based rehabilitation for coronary heart disease. Cochrane Database of Systematic Reviews 2001, Issue 1. [DOI: 10.1002/14651858.CD001800.] King 1998 King J, Crowe J. Mobilisation practices in Canadian critical care units. Physiotherapy Canada 1998;50(3):206-11. [MEDLINE: 0346574] Kouidi 2002 Kouidi E. Exercise training in dialysis patients: why, when, and how?. Artificial Organs 2002;26(12):1009-13. [PUBMED: 12460377] Krishnan 2002 Krishnan KR, Delong M, Kraemer H, Carney R, Spiegel D, Gordon C, et al.Comorbidity of depression with other medical diseases in the elderly. Biological Psychiatry 2002;52(6):559-88. [PUBMED: 12361669] Lavie 2009 Lavie CJ, Thomas RJ, Squires RW, Allison TG, Milani RV. Exercise training and cardiac rehabilitation in primary and secondary prevention of coronary heart disease. Mayo Clinic Proceedings 2009; 84(4):373-83. [PUBMED: 19339657] Lewis 2003 Lewis M. Intensive care unit rehabilitation within the United Kingdom: a review. Physiotherapy 2003;89(9):531-8. [DOI: 10.1016/S0031-9406(05)60179-4] Martin 2005 Martin M, Salim A, Murray J, Demetriades D, Belzberg H, Rhee P. The decreasing incidence and mortality of acute respiratory distress syndrome after injury: a 5-year observational study. Journal of Trauma 2005;50(5):1107-13. [PUBMED: 16385287] Mazzeo 2001 Mazzeo RS, Tanaka H. Exercise prescription for the elderly: current recommendations. Sports Medicine 2001;31(11):809-18. [PUBMED: 11583105] Miller 2002 Miller MD, Crotty M, Giles LC, Bannerman E, Whitehead C, Cobiac L, et al.Corrected arm muscle area: an independent predictor of long-term mortality in community dwelling older adults?. Journal of the America Geriatrics Society 2002;50(7): 1272-7. [PUBMED: 12133024] Paffenbarger 1986 Paffenbarger RS, Hyde RT, Wing AL, Hseih CC. Physical activity, all-cause mortality, and longevity of college alumni. New England Journal of Medicine 1986;314(10):605-13. [PUBMED: 3945246] Puhan 2006 Puhan MA, Busching G, Schunemann HJ, VanOort E, Zaugg C, Frey M. Interval versus continuous high-intensity exercise in chronic obstructive pulmonary disease: a randomized trial. Annals of Internal Medicine 2006;145(11):816-25. [PUBMED: 17146066] Rantanen 2000 Rantanen T, Harris T, Leveille SG, Visser M, Foley D, et al.Muscle strength and body mass index as long-term predictors of mortality in initially healthy men. Journal of Gerontology. Series A: Biological Sciences and Medical Sciences 2000;55(3):M168-73. [PUBMED: 10795731] RevMan 5.0 The Nordic Cochrane Centre, The Cochrane Collaboration. Review Manager (RevMan). 5.0. Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration, 2008. Schweickert 2009 Schweickert WD, Pohlman MC, Pohlman AS, Nigos C, Pawlik AJ, Esbrook CL, et al.Early physical and occupational therapy in mechanically ventilated, critically ill patients: a randomised controlled trial. Lancet 2009;373(epub):1874-82. [PUBMED: 19446324] Smith 2006 Smith TP, Kennedy SL, Smith M, Orent S, Fleshner M. Physiological improvements and health benefits during an exercisebased comprehensive rehabilitation program in medically complex patients. Exercise Immunology Review 2006;12:86-96. [PUBMED: 17201074] Stiller 2000 Stiller K. Physiotherapy in intensive care: toward an evidence-based practice. Chest 2000;118(6):1801-13. [PUBMED: 11115476] Storch 2008 Storch EK, Kruszynski DM. From rehabilitation to optimal function: role of clinical exercise therapy. Current Opinion in Critcal Care 2008;14(4):451-5. [PUBMED: 18614911] Wiles 2009 Wiles L, Stiller K. Passive limb movements for patients in an intensive care unit: A survey of physiotherapy practice in Australia. Journal of Critical Care 2009;epub:ahead of print. [PUBMED: 19819105] Yoshida 1999 Yoshida T, Kohzuki M, Yoshida K, Hiwatari M, Kamimoto M, Yamamoto C, et al.Physical and psychological improvements after phase II cardiac rehabilitation in patients with myocardial infarction. Nursing & Health Sciences 1999;1(3):163-70. [PUBMED: 10894639] Indicates the major publication for the study8pub1756pubArt.

The effects of reinforcement interval on the acquisition of paired-associate responses

Effects of reinforcement interval on acquisition of paired-associate response

Quantum Analogue Computing

We briefly review what a quantum computer is, what it promises to do for us, and why it is so hard to build one. Among the first applications anticipated to bear fruit is quantum simulation of quantum systems. While most quantum computation is an extension of classical digital computation, quantum simulation differs fundamentally in how the data is encoded in the quantum computer. To perform a quantum simulation, the Hilbert space of the system to be simulated is mapped directly onto the Hilbert space of the (logical) qubits in the quantum computer. This type of direct correspondence is how data is encoded in a classical analogue computer. There is no binary encoding, and increasing precision becomes exponentially costly: an extra bit of precision doubles the size of the computer. This has important consequences for both the precision and error correction requirements of quantum simulation, and significant open questions remain about its practicality. It also means that the quantum version of analogue computers, continuous variable quantum computers (CVQC) becomes an equally efficient architecture for quantum simulation. Lessons from past use of classical analogue computers can help us to build better quantum simulators in future.Comment: 10 pages, to appear in the Visions 2010 issue of Phil. Trans. Roy. Soc.

Novel six-coordinate Aryl- and Alkyltin complexes

Organo-tin compounds have wide applications as pesticides and as intermediates for organic synthesis.¹ They are invariably Sn(IV) derivatives and are generally four-coordinate.² The mixed organo/chioro compounds of the type RnSnCI4-n do however have the ability to expand their coordination numbers to five or six. This depends critically on the substituents - with four organic groups, R₄Sn, there is no tendency at all to coordinate extra ligands, while at the other extreme SnCl₄ readily forms six-coordinate [SnC1₄L₂] complexes since the electronegative halo groups increase the Lewis acidity of the tin centre

Velocity, energy and helicity of vortex knots and unknots

In this paper we determine the velocity, the energy and estimate writhe and twist helicity contributions of vortex filaments in the shape of torus knots and unknots (toroidal and poloidal coils) in a perfect fluid. Calculations are performed by numerical integration of the Biot-Savart law. Vortex complexity is parametrized by the winding number $w$, given by the ratio of the number of meridian wraps to that of the longitudinal wraps. We find that for $w<1$ vortex knots and toroidal coils move faster and carry more energy than a reference vortex ring of same size and circulation, whereas for $w>1$ knots and poloidal coils have approximately same speed and energy of the reference vortex ring. Helicity is dominated by the writhe contribution. Finally, we confirm the stabilizing effect of the Biot-Savart law for all knots and unknots tested, that are found to be structurally stable over a distance of several diameters. Our results also apply to quantized vortices in superfluid $^4$He.Comment: 17 pages, 8 figures, 2 table

Detection of a Moving Rigid Solid in a Perfect Fluid

In this paper, we consider a moving rigid solid immersed in a potential fluid. The fluid-solid system fills the whole two dimensional space and the fluid is assumed to be at rest at infinity. Our aim is to study the inverse problem, initially introduced in [3], that consists in recovering the position and the velocity of the solid assuming that the potential function is known at a given time. We show that this problem is in general ill-posed by providing counterexamples for which the same potential corresponds to different positions and velocities of a same solid. However, it is also possible to find solids having a specific shape, like ellipses for instance, for which the problem of detection admits a unique solution. Using complex analysis, we prove that the well-posedness of the inverse problem is equivalent to the solvability of an infinite set of nonlinear equations. This result allows us to show that when the solid enjoys some symmetry properties, it can be partially detected. Besides, for any solid, the velocity can always be recovered when both the potential function and the position are supposed to be known. Finally, we prove that by performing continuous measurements of the fluid potential over a time interval, we can always track the position of the solid.Comment: 19 pages, 14 figure