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Cessation Of X-Ray Pulsation Of Gx 1+4, W. Cui, B. Smith Jan 2004

Cessation Of X-Ray Pulsation Of Gx 1+4, W. Cui, B. Smith

Department of Physics and Astronomy Faculty Publications

We report results from our weekly monitoring campaign on the X-ray pulsar GX 1+4 with the Rossi X-Ray Timing Explorer satellite. The spin-down trend of GX 1+4 was continuing, with the pulsar being at its longest period ever measured (about 138.7 s). At the late stage of the campaign, the source entered an extended faint state, during which its X-ray (2-60 keV) flux decreased significantly, to an average level of similar to3 x 10(-10) ergs cm(-2) s(-1). It was highly variable in the faint state; the flux dropped to as low as similar to3 x 10(-11) ergs cm(-2) s(-1). in …

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Change In Speed And Direction Of The Jet Near The Core In The Quasar 3c 279, S. G. Jorstad, A. P. Marscher, M. L. Lister, A. M. Stirling, T. V. Cawthorne, J. L. Gomez, W. K. Gear Jan 2004

Change In Speed And Direction Of The Jet Near The Core In The Quasar 3c 279, S. G. Jorstad, A. P. Marscher, M. L. Lister, A. M. Stirling, T. V. Cawthorne, J. L. Gomez, W. K. Gear

Department of Physics and Astronomy Faculty Publications

Intensive monitoring of the innermost jet in the quasar 3C 279 at 43 GHz from 1998 March to 2001 April with the Very Long Baseline Array, in combination with previous observations, reveal ( 1) an increase in apparent speed from 5c to 17c and (2) a change in projected direction of the jet by similar to20degrees. These effects could result from a small increase in the intrinsic viewing angle of the jet nozzle from Thetaless than or similar to0.degrees5 to Thetaless than or similar to1.degrees6, with no increase required in the actual speed of the flow, which corresponds to a …

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A Search For Tev Gamma-Ray Emission From High-Peaked Flat-Spectrum Radio Quasars Using The Whipple Air Cerenkov Telescope, A. D. Falcone, I. H. Bond, P. J. Boyle, S. M. Bradbury, J. H. Buckley, D. Carter-Lewis, O. Celik, W. Cui, M. Daniel, M. D'Vali, I. D. Perez, C. Duke, D. J. Fegan, S. J. Fegan, J. P. Finley, L. F. Fortson, J. Gaidos, S. Gammell, K. Gibbs, G. H. Gillanders, J. Grube, J. Hall, T. A. Hall, D. Hanna, A. M. Hillas, J. Holder, D. Horan, A. Jarvis, G. E. Kenny, M. Kertzman, D. Kieda, J. Kildea, J. Knapp, K. Kosack, H. Krawczynski, F. Krennrich, M. J. Lang, S. Lebohec, E. Linton, J. Lloyd-Evans, A. Milovanovic, P. Moriarty, D. Muller, T. Nagai, S. Nolan, R. Ong, R. Pallassini, D. Petry, F. Pizlo, B. Power-Mooney, J. Quinn, M. Quinn, K. Ragan, P. Rebillot, P. T. Reynolds, H. J. Rose, M. Schroedter, G. Sembroski, S. P. Swordy, A. Syson, K. Tyler, V. V. Vassiliev, S. P. Wakely, G. Walker, T. C. Weekes, J. Zweerink Jan 2004

A Search For Tev Gamma-Ray Emission From High-Peaked Flat-Spectrum Radio Quasars Using The Whipple Air Cerenkov Telescope, A. D. Falcone, I. H. Bond, P. J. Boyle, S. M. Bradbury, J. H. Buckley, D. Carter-Lewis, O. Celik, W. Cui, M. Daniel, M. D'Vali, I. D. Perez, C. Duke, D. J. Fegan, S. J. Fegan, J. P. Finley, L. F. Fortson, J. Gaidos, S. Gammell, K. Gibbs, G. H. Gillanders, J. Grube, J. Hall, T. A. Hall, D. Hanna, A. M. Hillas, J. Holder, D. Horan, A. Jarvis, G. E. Kenny, M. Kertzman, D. Kieda, J. Kildea, J. Knapp, K. Kosack, H. Krawczynski, F. Krennrich, M. J. Lang, S. Lebohec, E. Linton, J. Lloyd-Evans, A. Milovanovic, P. Moriarty, D. Muller, T. Nagai, S. Nolan, R. Ong, R. Pallassini, D. Petry, F. Pizlo, B. Power-Mooney, J. Quinn, M. Quinn, K. Ragan, P. Rebillot, P. T. Reynolds, H. J. Rose, M. Schroedter, G. Sembroski, S. P. Swordy, A. Syson, K. Tyler, V. V. Vassiliev, S. P. Wakely, G. Walker, T. C. Weekes, J. Zweerink

Department of Physics and Astronomy Faculty Publications

Blazars have traditionally been separated into two broad categories based on their optical emission characteristics. Blazars with faint or no emission lines are referred to as BL Lacertae objects ( BL Lacs), and blazars with prominent, broad emission lines are commonly referred to as flat-spectrum radio quasars (FSRQs). The spectral energy distribution of FSRQs has generally been thought of as being more akin to the low-peaked BL Lacs, which exhibit a peak in the infrared region of the spectrum, as opposed to high-peaked BL Lacs (HBLs), which exhibit a peak in UV/X-ray region of the spectrum. All blazars that are …

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Constraints On The Very High Energy Emission From Bl Lacertae Objects, D. Horan, H. M. Badran, I. H. Bond, P. J. Boyle, S. M. Bradbury, J. H. Buckley, D. A. Carter-Lewis, M. Catanese, O. Celik, W. Cui, M. Daniel, M. D'Vali, I. D. C. Perez, C. Duke, A. Falcone, D. J. Fegan, S. J. Fegan, J. P. Finley, L. F. Fortson, J. A. Gaidos, S. Gammell, K. Gibbs, G. H. Gillanders, J. Grube, J. Hall, T. A. Hall, D. Hanna, A. M. Hillas, J. Holder, A. Jarvis, M. Jordan, G. E. Kenny, M. Kertzman, D. Kieda, J. Kildea, J. Knapp, K. Kosack, H. Krawczynski, F. Krennrich, M. J. Lang, S. Le Bohec, E. Linton, J. L. Evans, A. Milovanovic, P. Moriarty, D. Muller, T. Nagai, S. Nolan, R. A. Ong, R. Pallassini, D. Petry, B. Power-Mooney, J. Quinn, M. Quinn, K. Ragan, P. Rebillot, P. T. Reynolds, H. J. Rose, M. Schroedter, G. H. Sembroski, S. P. Swordy, A. Syson, V. V. Vassiliev, S. P. Wakely, G. Walker, T. C. Weekes, J. Zweerink Jan 2004

Constraints On The Very High Energy Emission From Bl Lacertae Objects, D. Horan, H. M. Badran, I. H. Bond, P. J. Boyle, S. M. Bradbury, J. H. Buckley, D. A. Carter-Lewis, M. Catanese, O. Celik, W. Cui, M. Daniel, M. D'Vali, I. D. C. Perez, C. Duke, A. Falcone, D. J. Fegan, S. J. Fegan, J. P. Finley, L. F. Fortson, J. A. Gaidos, S. Gammell, K. Gibbs, G. H. Gillanders, J. Grube, J. Hall, T. A. Hall, D. Hanna, A. M. Hillas, J. Holder, A. Jarvis, M. Jordan, G. E. Kenny, M. Kertzman, D. Kieda, J. Kildea, J. Knapp, K. Kosack, H. Krawczynski, F. Krennrich, M. J. Lang, S. Le Bohec, E. Linton, J. L. Evans, A. Milovanovic, P. Moriarty, D. Muller, T. Nagai, S. Nolan, R. A. Ong, R. Pallassini, D. Petry, B. Power-Mooney, J. Quinn, M. Quinn, K. Ragan, P. Rebillot, P. T. Reynolds, H. J. Rose, M. Schroedter, G. H. Sembroski, S. P. Swordy, A. Syson, V. V. Vassiliev, S. P. Wakely, G. Walker, T. C. Weekes, J. Zweerink

Department of Physics and Astronomy Faculty Publications

We present results from observations of 29 BL Lacertae objects, taken with the Whipple Observatory 10 m gamma-ray telescope between 1995 and 2000. The observed objects are mostly at low redshift (z<0.2), but observations of objects of up to z=0.444 are also reported. Five of the objects are EGRET sources and two are unconfirmed TeV sources. Three of the confirmed sources of extragalactic TeV gamma rays were originally observed as part of this survey and have been reported elsewhere. No significant excesses are detected from any of the other objects observed, on timescales of days, months, or years. We report 99.9% confidence level flux upper limits for the objects for each observing season. The flux upper limits are typically 20% of the Crab flux, although for some sources, limits as sensitive as 6% of the Crab flux were derived. The results are consistent with the synchrotron self-Compton model predictions considered in this work.

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Tev Gamma-Ray Observations Of The Galactic Center, K. Kosack, H. M. Badran, I. H. Bond, P. J. Boyle, S. M. Bradbury, J. H. Buckley, D. A. Carter-Lewis, O. Celik, V. Connaughton, W. Cui, M. Daniel, M. D'Vall, I. D. L. Perez, C. Duke, A. Falcone, D. J. Fegan, S. J. Fegan, J. P. Finley, L. F. Fortson, J. A. Gaidos, S. Gammell, K. Gibbs, G. H. Gillanders, J. Grube, K. Gutierrez, J. Hall, T. A. Hall, D. Hanna, A. M. Hillas, J. Holder, D. Horan, A. Jarvis, M. Jordan, G. E. Kenny, M. Kertzman, D. Kieda, J. Kildea, J. Knapp, H. Krawczynski, F. Krennrich, M. J. Lang, S. Le Bohec, E. Linton, J. Lloyd-Evans, A. Milovanovic, J. Mcenery, R. Moriarty, D. Muller, T. Nagai, S. Nolan, R. A. Ong, R. Pallassini, D. Petry, B. Power-Mooney, J. Quinn, M. Quinn, K. Ragan, P. Rebillot, P. T. Reynolds, H. J. Rose, M. Schroedter, G. H. Sembroski, S. P. Swordy, A. Syson, V. V. Vassiliev, S. P. Wakely, G. Walker, T. C. Weekes, J. Zweerink Jan 2004

Tev Gamma-Ray Observations Of The Galactic Center, K. Kosack, H. M. Badran, I. H. Bond, P. J. Boyle, S. M. Bradbury, J. H. Buckley, D. A. Carter-Lewis, O. Celik, V. Connaughton, W. Cui, M. Daniel, M. D'Vall, I. D. L. Perez, C. Duke, A. Falcone, D. J. Fegan, S. J. Fegan, J. P. Finley, L. F. Fortson, J. A. Gaidos, S. Gammell, K. Gibbs, G. H. Gillanders, J. Grube, K. Gutierrez, J. Hall, T. A. Hall, D. Hanna, A. M. Hillas, J. Holder, D. Horan, A. Jarvis, M. Jordan, G. E. Kenny, M. Kertzman, D. Kieda, J. Kildea, J. Knapp, H. Krawczynski, F. Krennrich, M. J. Lang, S. Le Bohec, E. Linton, J. Lloyd-Evans, A. Milovanovic, J. Mcenery, R. Moriarty, D. Muller, T. Nagai, S. Nolan, R. A. Ong, R. Pallassini, D. Petry, B. Power-Mooney, J. Quinn, M. Quinn, K. Ragan, P. Rebillot, P. T. Reynolds, H. J. Rose, M. Schroedter, G. H. Sembroski, S. P. Swordy, A. Syson, V. V. Vassiliev, S. P. Wakely, G. Walker, T. C. Weekes, J. Zweerink

Department of Physics and Astronomy Faculty Publications

We report a possible detection of TeV gamma rays from the Galactic center by the Whipple 10 m gamma-ray telescope. Twenty-six hours of data were taken over an extended period from 1995 through 2003 resulting in a total significance of 3.7 sigma. The measured excess corresponds to an integral flux of 1.6 x 10(-8) +/- 0.5 x 10(-8) (stat) +/- 0.3 x 10(-8) (sys) photons m(-2) s(-1) above an energy of 2.8 TeV, roughly 40% of the flux from the Crab Nebula at this energy. The 95% confidence region has an angular extent of about 15' and includes the position …

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The Vsop 5 Ghz Active Galactic Nucleus Survey. Ii. Data Calibration And Imaging, J. E. J. Lovell, G. A. Moellenbrock, S. Horiuchi, E. B. Fomalont, W. K. Scott, H. Hirabayashi, R. G. Dodson, S. M. Dougherty, P. G. Edwards, S. Frey, L. I. Gurvits, M. L. Lister, D. W. Murphy, Z. Paragi, B. G. Piner, Z. Q. Shen, A. R. Taylor, S. J. Tingay, Y. Asaki, D. Moffett, Y. Murata Jan 2004

The Vsop 5 Ghz Active Galactic Nucleus Survey. Ii. Data Calibration And Imaging, J. E. J. Lovell, G. A. Moellenbrock, S. Horiuchi, E. B. Fomalont, W. K. Scott, H. Hirabayashi, R. G. Dodson, S. M. Dougherty, P. G. Edwards, S. Frey, L. I. Gurvits, M. L. Lister, D. W. Murphy, Z. Paragi, B. G. Piner, Z. Q. Shen, A. R. Taylor, S. J. Tingay, Y. Asaki, D. Moffett, Y. Murata

Department of Physics and Astronomy Faculty Publications

The VLBI Space Observatory Programme (VSOP) mission is a Japanese-led project to study radio sources with sub-milliarcsecond angular resolution using an orbiting 8 m telescope, HALCA, and global arrays of Earth-based telescopes. Approximately 25% of the observing time has been devoted to a survey of compact active galactic nuclei (AGNs) at 5 GHz that are stronger than 1 Jy-the VSOP AGN Survey. This paper, the second in a series, describes the data calibration, source detection, self-calibration, imaging, and modeling and gives examples illustrating the problems specific to space VLBI. The VSOP Survey Web site, which contains all results and calibrated …

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Electrochromic Shift Of Chlorophyll Absorption In Photosystem I From Synechocystis Sp Pcc 6803: A Probe Of Optical And Dielectric Properties Around The Secondary Electron Acceptor, N. Dashdorj, W. Xu, P. Martinsson, P. R. Chitnis, S. Savikhin Jan 2004

Electrochromic Shift Of Chlorophyll Absorption In Photosystem I From Synechocystis Sp Pcc 6803: A Probe Of Optical And Dielectric Properties Around The Secondary Electron Acceptor, N. Dashdorj, W. Xu, P. Martinsson, P. R. Chitnis, S. Savikhin

Department of Physics and Astronomy Faculty Publications

Nanosecond absorption dynamics at similar to685 nm after excitation of photosystem I ( PS I) from Synechocystis sp. PCC 6803 is consistent with electrochromic shift of absorption bands of the Chl a pigments in the vicinity of the secondary electron acceptor A(1). Based on experimental optical data and structure-based simulations, the effective local dielectric constant has been estimated to be between 3 and 20, which suggests that electron transfer in PS I is accompanied by considerable protein relaxation. Similar effective dielectric constant values have been previously observed for the bacterial photosynthetic reaction center and indicate that protein reorganization leading to …

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Cdf Run Iib Silicon Detector: The Innermost Layer, P. Merkel, P. Azzi, N. Bacchetta, D. Bisello, G. Busetto, K. Hara, S. Kim, C. Manea, Z. Wang, S. Behari, P. Maksimovic, D. Benjamin, S. Cabrera, M. Kruse, G. Bolla, D. Bortoletto, A. Canepa, J. P. Fernandez, P. Booth, P. Cooke, M. Cascella, G. Cardoso, G. Derylo, B. Flaugher, M. Hrycyk, N. Kuznetsova, P. Lukens, T. Nelson, Y. Orlov, W. Wester, J. C. Yun, M. Chertok, B. Holbrook, R. Lander, T. Landry, D. Pellett, A. Soha, W. Yao, C. I. Ciobanu, T. Junk, E. J. Feng, J. Freeman, L. Galtieri, M. Garcia-Sciveres, C. Haber, P. J. Lujan, E. Mandelli, M. Weber, W. Yao, F. Zetti, S. Zimmermann, J. Goldstein, R. Harr, C. Hill, A. Himmel, J. Incandela, D. Stuart, K. Kobayashi, I. Nakano, R. Tanaka, D. J. Kong, Y. C. Yang, R. Lauhakangas, R. Orava, K. Osterberg, R. S. Lu, S. N. Min, T. Okusawa, K. Yamamoto, M. Tavi, S. Zucchelli, S. C. Hong, E. J. Jeon, K. K. Joo, J. Lee Jan 2004

Cdf Run Iib Silicon Detector: The Innermost Layer, P. Merkel, P. Azzi, N. Bacchetta, D. Bisello, G. Busetto, K. Hara, S. Kim, C. Manea, Z. Wang, S. Behari, P. Maksimovic, D. Benjamin, S. Cabrera, M. Kruse, G. Bolla, D. Bortoletto, A. Canepa, J. P. Fernandez, P. Booth, P. Cooke, M. Cascella, G. Cardoso, G. Derylo, B. Flaugher, M. Hrycyk, N. Kuznetsova, P. Lukens, T. Nelson, Y. Orlov, W. Wester, J. C. Yun, M. Chertok, B. Holbrook, R. Lander, T. Landry, D. Pellett, A. Soha, W. Yao, C. I. Ciobanu, T. Junk, E. J. Feng, J. Freeman, L. Galtieri, M. Garcia-Sciveres, C. Haber, P. J. Lujan, E. Mandelli, M. Weber, W. Yao, F. Zetti, S. Zimmermann, J. Goldstein, R. Harr, C. Hill, A. Himmel, J. Incandela, D. Stuart, K. Kobayashi, I. Nakano, R. Tanaka, D. J. Kong, Y. C. Yang, R. Lauhakangas, R. Orava, K. Osterberg, R. S. Lu, S. N. Min, T. Okusawa, K. Yamamoto, M. Tavi, S. Zucchelli, S. C. Hong, E. J. Jeon, K. K. Joo, J. Lee

Department of Physics and Astronomy Faculty Publications

The innermost layer (L00) of the Run IIa silicon detector of CDF was planned to be replaced for the high luminosity Tevatron upgrade of Run IIb. This new silicon layer (L0) is designed to be a radiation tolerant replacement for the otherwise very similar L00 from Run IIa. The data are read out via long, fine-pitch, low-mass cables allowing the hybrids with the chips to sit at higher z(similar to 70 cm), outside of the tracking volume. The design and first results from the prototyping phase are presented. Special focus is placed on the amount and the structure of induced …

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Secure Group Communication Using Robust Contributory Key Agreement, Y. Amir, Y. Kim, C. Nita-Rotaru, J. L. Schultz, J. Stanton, G. Tsudik Jan 2004

Secure Group Communication Using Robust Contributory Key Agreement, Y. Amir, Y. Kim, C. Nita-Rotaru, J. L. Schultz, J. Stanton, G. Tsudik

Department of Physics and Astronomy Faculty Publications

Contributory group key agreement protocols generate group keys based on contributions of all group members. Particularly appropriate for relatively small collaborative peer groups, these protocols are resilient to many types of attacks. Unlike most group key distribution protocols, contributory group key agreement protocols offer strong security properties such as key independence and perfect forward secrecy. This paper presents the first robust contributory key agreement protocol resilient to any sequence of group changes. The protocol, based on the Group Diffie-Hellman contributory key agreement, uses the services of a group communication system supporting Virtual Synchrony semantics. We prove that it provides both …

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Precise Determination Of The Casimir Force And First Realization Of A "Casimir Less" Experiment, R. S. Decca, D. Lopez, H. B. Chan, E. Fischbach, G. L. Klimchitskaya, D. E. Krause, V. M. Mostepanenkot Jan 2004

Precise Determination Of The Casimir Force And First Realization Of A "Casimir Less" Experiment, R. S. Decca, D. Lopez, H. B. Chan, E. Fischbach, G. L. Klimchitskaya, D. E. Krause, V. M. Mostepanenkot

Department of Physics and Astronomy Faculty Publications

We present improved Casimir effect measurements. The attractive force between a metallized sphere and the coated plate of a Si microelectro mechanical oscillator is measured with unparalleled precision. The same setup, but in a dynamic scheme, yields a determination of the Casimir pressure between two infinite plates. Since the Casimir force is the dominant interaction in the 0.11 mum range under these experimental conditions, it acts as a background in the search for new forces in the submicrometer range. We report our progress in the realization of an experiment where the effect of the Casimir force is minimized (a "Casimir-less" …

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Nonlinear Tapping Dynamics Of Multi-Walled Carbon Nanotube Tipped Atomic Force Microcantilevers, S. I. Lee, S. W. Howell, A. Raman, R. Reifenberger, C. V. Nguyen, M. Meyyappan Jan 2004

Nonlinear Tapping Dynamics Of Multi-Walled Carbon Nanotube Tipped Atomic Force Microcantilevers, S. I. Lee, S. W. Howell, A. Raman, R. Reifenberger, C. V. Nguyen, M. Meyyappan

Department of Physics and Astronomy Faculty Publications

The nonlinear dynamics of an atomic force microcantilever (AFM) with an attached multi-walled carbon nanotube (MWCNT) tip is investigated experimentally and theoretically. We present the experimental nonlinear frequency response of a MWCNT tipped microcantilever in the tapping mode. Several unusual features in the response distinguish it from those traditionally observed for conventional tips. The MWCNT tipped AFM probe is apparently immune to conventional imaging instabilities related to the coexistence of attractive and repulsive tapping regimes. A theoretical interaction model for the system using an Euler elastica MWCNT model is developed and found to predict several unusual features of the measured …

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Meta-Analysis Of Two-Treatment Clinical Trials Including Both Continuous And Dichotomous Results, Charles F. Babbs Jan 2004

Meta-Analysis Of Two-Treatment Clinical Trials Including Both Continuous And Dichotomous Results, Charles F. Babbs

Weldon School of Biomedical Engineering Faculty Publications

To expedite the timely creation of medical practice guidelines, a meta-analytic method was developed to combine of both dichotomous survival data and continuous physiologic data from multiple studies comparing the same innovative clinical intervention to standard care. The method is adapted for synthesis of small, early studies of novel treatments. An aggregate ratio, R*, of the observed treatment effect to a clinically optimal treatment effect for studies in a series is computed, and compared to the 95% confidence limit for R* under the null hypothesis. Weights assigned to each study may reflect its precision, quality, or clinical relevance. Input data …

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Boundary Layer Leakage Model, Jan Prins Jan 2004

Boundary Layer Leakage Model, Jan Prins

International Compressor Engineering Conference

No abstract provided.

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High Efficiency Pressure Oscillator For Low-Temperature Pulse Tube Cryocooler, Kyle B. Wilson, Reuven J. Unger Jan 2004

High Efficiency Pressure Oscillator For Low-Temperature Pulse Tube Cryocooler, Kyle B. Wilson, Reuven J. Unger

International Compressor Engineering Conference

No abstract provided.

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Three-Dimension Numerical Simulation Of Discharge Flow In A Scroll Air Compressor, Jian Mei Feng, Zong Chang Qu, Xin Wei Lin Jan 2004

Three-Dimension Numerical Simulation Of Discharge Flow In A Scroll Air Compressor, Jian Mei Feng, Zong Chang Qu, Xin Wei Lin

International Compressor Engineering Conference

No abstract provided.

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Extending The Operation Range Of Dry Screw Compressors By Cooling Their Rotors, Nikola Stosic, Ian K. Smith, Ahmed Kovacevic Jan 2004

Extending The Operation Range Of Dry Screw Compressors By Cooling Their Rotors, Nikola Stosic, Ian K. Smith, Ahmed Kovacevic

International Compressor Engineering Conference

No abstract provided.

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Single-Phase Flow And Heat Transport And Pumping Considerations In Microchannel Heat Sinks, S V. Garimella, Vishal Singhal Jan 2004

Single-Phase Flow And Heat Transport And Pumping Considerations In Microchannel Heat Sinks, S V. Garimella, Vishal Singhal

CTRC Research Publications

Microchannel heat sinks are widely regarded as being among the most effective heat removal techniques from space-constrained electronic devices. However, the fluid flow and heat transfer in microchannels is not fully understood. The pumping requirements for flow through microchannels are also very high, and none of the micropumps in the literature is truly suitable for this application. Results are reported from a wide-ranging research program being conducted on microchannel heat sinks and micropumps to understand fluid flow and heat transfer in microchannels and to identify pumping requirements and suitable mechanisms for pumping in microchannels. In particular, experiments have been performed …

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Simulation Of Ion Generation And Breakdown In Atmospheric Air, W. Zhang, T. S. Fisher, S V. Garimella Jan 2004

Simulation Of Ion Generation And Breakdown In Atmospheric Air, W. Zhang, T. S. Fisher, S V. Garimella

CTRC Research Publications

Understanding of ion generation in air provides insights to several applications, such as gas sensors, electrohydrodynamic pumping, and air purification. In this paper, ion generation processes in atmospheric air are simulated using a particle-in-cell and Monte Carlo method with emphasis on the prediction of ion generation and breakdown characteristics in microscale gaps. The simulation results are validated through comparison to Townsend’s discharge theory and experiments. The significance of each relevant electron-molecule reaction is characterized to improve understanding of ion generation dynamics. Self-sustaining discharge and ionization are predicted under sufficient voltage bias, and the predicted trends of breakdown voltage are similar …

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Investigation Of Liquid Flow In Microchannels, D. Liu, S V. Garimella Jan 2004

Investigation Of Liquid Flow In Microchannels, D. Liu, S V. Garimella

CTRC Research Publications

Liquid flow in microchannels is investigated both experimentally and numerically in this work. The experiments are carried out in microchannels with hydraulic diameters from 244 to 974 m at Reynolds numbers ranging from 230 to 6500. The pressure drop in these microchannels is measured in situ, and is also determined by correcting global measurements for inlet and exit losses. Onset of turbulence is verified by flow visualization. The experimental measurements of pressure drop are compared to numerical predictions. Results from this work show that conventional theory may be used to successfully predict the flow behavior in microchannels in the range …

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High-Field Quasi-Ballistic Transport In Short Carbon Nanotubes, Ali Javey, Jing Guo, Magnus Paulsson, Qian Wang, Mark S. Lundstrom, Hongjie Dai, David Mann Jan 2004

High-Field Quasi-Ballistic Transport In Short Carbon Nanotubes, Ali Javey, Jing Guo, Magnus Paulsson, Qian Wang, Mark S. Lundstrom, Hongjie Dai, David Mann

Department of Electrical and Computer Engineering Faculty Publications

Single walled carbon nanotubes with Pd Ohmic contacts and lengths ranging from several microns down to 10 nm are investigated by electron transport experiments and theory. The mean-free path (MFP) for acoustic phonon scattering is estimated to be lap ~300  nm, and that for optical phonon scattering is lop ~15  nm. Transport through very short (~10  nm) nanotubes is free of significant acoustic and optical phonon scattering and thus ballistic and quasiballistic at the low- and high-bias voltage limits, respectively. High currents of up to 70   μA can flow through a short nanotube. Possible mechanisms for the eventual electrical breakdown …

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A Three-Dimensional Quantum Simulation Of Silicon Nanowire Transistors With The Effective Mass Approximation, Jing Wang, Eric Polizzi, Mark S. Lundstrom Jan 2004

A Three-Dimensional Quantum Simulation Of Silicon Nanowire Transistors With The Effective Mass Approximation, Jing Wang, Eric Polizzi, Mark S. Lundstrom

Department of Electrical and Computer Engineering Faculty Publications

The silicon nanowire transistor (SNWT) is a promising device structure for future integrated circuits, and simulations will be important for understanding its device physics and assessing its ultimate performance limits. In this work, we present a three-dimensional (3D) quantum mechanical simulation approach to treat various SNWTs within the effective-mass approximation. We begin by assuming ballistic transport, which gives the upper performance limit of the devices. The use of a mode space approach (either coupled or uncoupled) produces high computational efficiency that makes our 3D quantum simulator practical for extensive device simulation and design. Scattering in SNWTs is then treated by …

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Analysis Of A Phase Change Energy Storage System For Pulsed Power Dissipation, S Krishnan, S V. Garimella Jan 2004

Analysis Of A Phase Change Energy Storage System For Pulsed Power Dissipation, S Krishnan, S V. Garimella

CTRC Research Publications

The melting of a phase change material in a container of rectangular cross-section with multiple discrete heat sources mounted on one side is investigated for electronics cooling by latent heat energy storage. This numerical study focuses on the thermal management issues that arise when electronic components experience sudden surges in power dissipation. The transient response of the energy storage system to short pulses in power dissipation is studied. Convective cooling using air-cooled heat sinks on the sides of the containment remote from the heat sources provides for heat rejection to ambient air. The analysis is performed under different pulse frequencies. …

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Thermal Management Of Transient Power Spikes In Electronics - Phase Change Energy Storage Or Copper Heat Sinks?, S. Krishnan, S V. Garimella Jan 2004

Thermal Management Of Transient Power Spikes In Electronics - Phase Change Energy Storage Or Copper Heat Sinks?, S. Krishnan, S V. Garimella

CTRC Research Publications

A transient thermal analysis is performed to investigate thermal control of power semiconductors using phase change materials, and to compare the performance of this approach to that of copper heat sinks. Both the melting of the phase change material under a transient power spike input, as well as the resolidification process, are considered. Phase change materials of different kinds (paraffin waxes and metallic alloys) are considered, with and without the use of thermal conductivity enhancers. Simple expressions for the melt depth, melting time and temperature distribution are presented in terms of the dimensions of the heat sink and the thermophysical …

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A Two-Temperature Model For The Analysis Of Passive Thermal Control Systems, S. Krishnan, J. Y. Murthy, S V. Garimella Jan 2004

A Two-Temperature Model For The Analysis Of Passive Thermal Control Systems, S. Krishnan, J. Y. Murthy, S V. Garimella

CTRC Research Publications

Passive control of steady and unsteady thermal loads using effective thermal conductivity enhancers, such as metal foams, internal fins and metal filler particles, is being explored for a variety of electronics applications. The interstices are filled with air, phase change materials, or other fluids. Local thermal equilibrium between the solid filler and the matrix is not ensured in such systems since their thermal diffusivities are frequently very different. The use of a single volume-averaged energy equation for both the phases cannot be justified in such situations. A two-medium approach is used in the present work to account for the local …

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Design Of Flapper Valves For A Co2 Commercial Refrigeration Compressor, Douglas A. Collings, Thomas J. Weadock Jan 2004

Design Of Flapper Valves For A Co2 Commercial Refrigeration Compressor, Douglas A. Collings, Thomas J. Weadock

International Compressor Engineering Conference

No abstract provided.

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Optimizing Chest Compression To Rescue Ventilation Ratios During One-Rescuer Cpr By Professionals And Lay Persons: Children Are Not Just Little Adults, Charles F. Babbs, Vinay Nadkarni Jan 2004

Optimizing Chest Compression To Rescue Ventilation Ratios During One-Rescuer Cpr By Professionals And Lay Persons: Children Are Not Just Little Adults, Charles F. Babbs, Vinay Nadkarni

Weldon School of Biomedical Engineering Faculty Publications

Objective: To estimate the optimum ratio of chest compressions to ventilations for onerescuer CPR that maximizes systemic oxygen delivery in children. Method: Equations describing oxygen delivery and blood flow during CPR as functions of the number of compressions and the number of ventilations delivered over time were adapted from the former work of Babbs and Kern. These equations were solved explicitly as a function of body weight, using scaling algorithms based upon principles of developmental anatomy and physiology. Results: The optimal compression to ventilation (C/V) ratios for infants and younger children increase sharply as a function of body weight. Optimal …

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Thermal And Fluid Dynamic Behavior Of Trans-Critical Carbon Dioxide Hermetic Reciprocating Compressors: Numerical Analysis, Carlos D. Perã©Z Segarra, Joaquim Rigola, Assensi Oliva Jan 2004

Thermal And Fluid Dynamic Behavior Of Trans-Critical Carbon Dioxide Hermetic Reciprocating Compressors: Numerical Analysis, Carlos D. Perã©Z Segarra, Joaquim Rigola, Assensi Oliva

International Compressor Engineering Conference

No abstract provided.

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Turbo Water Chiller With Water As Refrigerant, Eberhard Wobst, Nikolai Kalitzin, Rainer Apley Jan 2004

Turbo Water Chiller With Water As Refrigerant, Eberhard Wobst, Nikolai Kalitzin, Rainer Apley

International Compressor Engineering Conference

No abstract provided.

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Conceptual Design Study Of A Supersonic Compressor Applied To Refrigerant Compression Cycles, Shawn P. Lawlor, Paul M. Brown, Steven G. Mackin Jan 2004

Conceptual Design Study Of A Supersonic Compressor Applied To Refrigerant Compression Cycles, Shawn P. Lawlor, Paul M. Brown, Steven G. Mackin

International Compressor Engineering Conference

No abstract provided.

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Performance Study Of A 3-Ton Residential Co2 A/C System With A Variable Flow Rate Co2 Compressor, Rodney A. Hugelman Jan 2004

Performance Study Of A 3-Ton Residential Co2 A/C System With A Variable Flow Rate Co2 Compressor, Rodney A. Hugelman

International Compressor Engineering Conference

No abstract provided.

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