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Ting A, Jiki M, Bell C, Murray C, Mughal Z, Child F. S27 Should routine screening for vitamin d deficiency be incorporated into current guidelines for treatment of paediatric TB patients? Thorax 2010. [DOI: 10.1136/thx.2010.150912.27] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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Helle MH, Kaganovich D, Gordon DF, Ting A. Measurement of electro-optic shock and electron acceleration in a strongly cavitated laser wakefield accelerator. PHYSICAL REVIEW LETTERS 2010; 105:105001. [PMID: 20867524 DOI: 10.1103/physrevlett.105.105001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2010] [Indexed: 05/29/2023]
Abstract
Conically emitted second harmonic radiation was observed when a relativistically intense, ultrashort laser pulse was focused into a jet of gas. This second harmonic electro-optic shock is the result of frequency mixing within the sheath of electrons surrounding a highly cavitated plasma region created by the ponderomotive force of the laser. Strong correlation between the second harmonic characteristics and electron acceleration has been observed.
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Gordon DF, Hafizi B, Ting A. Nonlinear conversion of photon spin to photon orbital angular momentum. OPTICS LETTERS 2009; 34:3280-3282. [PMID: 19881567 DOI: 10.1364/ol.34.003280] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
A relativistically intense, ultrashort laser pulse with purely spin angular momentum produces second-harmonic radiation with equal parts of both spin and orbital angular momentum when focused into a plasma. The orbital contribution is due to an azimuthal phase variation that arises in the nonlinear current density. This phase variation is associated with the radial nonuniformity driven by ponderomotive blowout.
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Ting A, James M, Woodfield DG, Morris PJ. The distribution of HL-A antigens in the coastal populations of Papua New Guinea. TISSUE ANTIGENS 2008; 2:409-14. [PMID: 4648383 DOI: 10.1111/j.1399-0039.1972.tb00061.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Morris PJ, Ting A, Alpers MP, Simons M. Leukocyte antigens in a New Guinea population. TISSUE ANTIGENS 2008; 1:49-52. [PMID: 5154367 DOI: 10.1111/j.1399-0039.1971.tb00077.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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Ting A, Wee GB, Simons MJ, Morris PJ. The distribution of HL-A leukocyte antigens in Singapore Chinese, Malays, and Indians. TISSUE ANTIGENS 2008; 1:258-64. [PMID: 5154531 DOI: 10.1111/j.1399-0039.1971.tb00103.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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Gordon DF, Hafizi B, Kaganovich D, Ting A. Electro-optic shocks from ultraintense laser-plasma interactions. PHYSICAL REVIEW LETTERS 2008; 101:045004. [PMID: 18764337 DOI: 10.1103/physrevlett.101.045004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2008] [Indexed: 05/26/2023]
Abstract
Second harmonic radiation in the form of an electro-optic shock is produced in the blowout regime of a laser wakefield in a plasma. The shock is produced by the interaction between the laser field and the electron sheath surrounding the electron cavitation region. Because the sheath is thin, phase matching is unimportant, and the radiated energy grows secularly with the interaction length. The angle of emission is given by the Cherenkov angle associated with the ratio of the second harmonic phase velocity to the fundamental phase velocity. The shock formation is investigated in three dimensions via analysis and particle-in-cell simulations.
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Kaganovich D, Gordon DF, Ting A. Observation of large-angle quasimonoenergetic electrons from a laser wakefield. PHYSICAL REVIEW LETTERS 2008; 100:215002. [PMID: 18518612 DOI: 10.1103/physrevlett.100.215002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2008] [Indexed: 05/26/2023]
Abstract
A relativistically intense laser pulse is focused into a helium jet and quasimonoenergetic electrons emitted at a 40 degrees angle with respect to the laser axis are observed. The average electron energy is between 1 and 2 MeV and the total accelerated charge is about 1 nC emitted in a 10 degrees cone angle. Three dimensional particle-in-cell simulations reproduce key features of the experimental results and show that the interaction between ionization heating and nonlinear cavitation wakefields is responsible for the acceleration.
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Champeaux S, Bergé L, Gordon D, Ting A, Peñano J, Sprangle P. (3+1)-dimensional numerical simulations of femtosecond laser filaments in air: toward a quantitative agreement with experiments. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 77:036406. [PMID: 18517532 DOI: 10.1103/physreve.77.036406] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2007] [Revised: 12/19/2007] [Indexed: 05/26/2023]
Abstract
Three-dimensional numerical simulations and direct experimental measurements of the multifilamentation of femtosecond laser pulses propagating in air are quantitatively compared. Agreement is obtained in terms of the evolution of the filamentation pattern and in terms of the size and energy of the individual filaments through 12 m of propagation. These results are made possible by the combination of a massively parallel propagation code along with a nondestructive experimental diagnostic technique. Influence of the pulse duration is moreover addressed. The numerical calculations also show that single and multiple filaments exhibit almost identical spectral signature.
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Chan S, Yong X, Ting A, Kendrick M, DeWitt DE. Rural healthcare provider opinions about implementation of an after-hours rural telephone triage system. Rural Remote Health 2007; 7:656. [PMID: 17367244] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/14/2023] Open
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Song J, Hanniford D, Doucette C, Graham E, Poole MF, Ting A, Sherf B, Harrington J, Brunden K, Stricker-Krongrad A. Development of homogeneous high-affinity agonist binding assays for 5-HT2 receptor subtypes. Assay Drug Dev Technol 2006; 3:649-59. [PMID: 16438660 DOI: 10.1089/adt.2005.3.649] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The serotonin (5-hydroxytryptamine) 5-HT2 receptor subfamily consists of three members, 5-HT2A, 5-HT2B, and 5-HT2C. These receptors share high homology in their amino acid sequence, have similar signaling pathways, and have been indicated to play important roles in feeding, anxiety, aggression, sexual behavior, mood, and pain. Subtype-selective agonists and antagonists have been explored as drugs for hypertension, Parkinson's disease, sleep disorders, anxiety, depression, schizophrenia, and obesity. In this study, we report the development of homogeneous agonist binding assays in a scintillation proximity assay (SPA) format to determine the high-affinity binding state of agonist compounds for the human 5-HT2C, 5-HT2A, and 5-HT2B receptors. The 5-HT2 agonist 1-(4- [125I]iodo-2,5-dimethoxyphenyl)-2-aminopropane ([125I]DOI) was used to label the high-affinity sites for the 5-HT2A and 5-HT2C receptors. The high-affinity sites for the 5-HT2B receptor were labeled with [3H]lysergic acid diethylamide. Total receptor expression was determined with the 5-HT2 antagonist [3H]mesulergine for the 5-HT2B and 5-HT2C receptors, and [3H]ketanserin for the 5-HT2A receptor. The agonist high-affinity binding sites accounted for 2.3% (5-HT(2C) receptor), 4.0% (5-HT2A receptor), and 22% (5-HT2B receptor) of the total receptor population. Competition binding studies using known agonists indicated high Z' values of the agonist binding assays in SPA format (Z' > 0.70). The Ki values of 5-HT, (R)(-)DOI, and VER-3323 for the 5-HT2A, 5-HT2B, and 5-HT2C receptors by SPA format were equivalent to published data determined by filtration binding assays. These results indicate that agonist binding assays in SPA format can be easily adapted to a high throughput assay to screen for selective 5-HT2C receptor agonists, as well as for selectivity profiling of the compounds.
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MESH Headings
- Amphetamines/pharmacology
- Binding, Competitive
- Calcium Signaling/drug effects
- Cell Line
- Dose-Response Relationship, Drug
- Drug Evaluation, Preclinical/methods
- Ergolines/metabolism
- Humans
- Ketanserin/metabolism
- Lysergic Acid Diethylamide/pharmacology
- Radioligand Assay
- Receptor, Serotonin, 5-HT2A/analysis
- Receptor, Serotonin, 5-HT2A/metabolism
- Receptor, Serotonin, 5-HT2B/analysis
- Receptor, Serotonin, 5-HT2B/metabolism
- Receptor, Serotonin, 5-HT2C/analysis
- Receptor, Serotonin, 5-HT2C/metabolism
- Serotonin/pharmacology
- Serotonin 5-HT2 Receptor Agonists
- Serotonin Antagonists/metabolism
- Serotonin Receptor Agonists/pharmacology
- Transfection
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Kimura WD, Andreev NE, Babzien M, Ben-Zvi I, Cline DB, Dilley CE, Gottschalk SC, Hooker SM, Kusche KP, Kuznetsov SV, Pavlishin IV, Pogorelsky IV, Pogosova AA, Steinhauer LC, Ting A, Yakimenko V, Zigler A, Zhou F. Inverse free electron lasers and laser wakefield acceleration driven by CO2 lasers. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2006; 364:611-22. [PMID: 16483952 DOI: 10.1098/rsta.2005.1726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The staged electron laser acceleration (STELLA) experiment demonstrated staging between two laser-driven devices, high trapping efficiency of microbunches within the accelerating field and narrow energy spread during laser acceleration. These are important for practical laser-driven accelerators. STELLA used inverse free electron lasers, which were chosen primarily for convenience. Nevertheless, the STELLA approach can be applied to other laser acceleration methods, in particular, laser-driven plasma accelerators. STELLA is now conducting experiments on laser wakefield acceleration (LWFA). Two novel LWFA approaches are being investigated. In the first one, called pseudo-resonant LWFA, a laser pulse enters a low-density plasma where nonlinear laser/plasma interactions cause the laser pulse shape to steepen, thereby creating strong wakefields. A witness e-beam pulse probes the wakefields. The second one, called seeded self-modulated LWFA, involves sending a seed e-beam pulse into the plasma to initiate wakefield formation. These wakefields are amplified by a laser pulse following shortly after the seed pulse. A second e-beam pulse (witness) follows the seed pulse to probe the wakefields. These LWFA experiments will also be the first ones driven by a CO(2) laser beam.
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Nunn A, McLeod J, Brown L, Hall C, Orr B, Brown I, Ting A, Hayes C, Earley P, Hawkins R. Monitoring spinal cord injured patients during activity using a datalogger: Preliminary results. ACTA ACUST UNITED AC 2005. [DOI: 10.3233/tad-2005-17204] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Gordon DF, Hubbard RF, Cooley JH, Hafizi B, Ting A, Sprangle P. Quasimonoenergetic electrons from unphased injection into channel guided laser wakefield accelerators. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2005; 71:026404. [PMID: 15783426 DOI: 10.1103/physreve.71.026404] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2004] [Revised: 11/11/2004] [Indexed: 05/24/2023]
Abstract
A high-quality electron beam can be extracted from a channel guided laser wakefield accelerator without confining the injected particles to a small region of phase. By careful choice of the injection energy, a regime can be found where uniformly phased particles are quickly bunched by the accelerator itself and subsequently accelerated to high energy. The process is particularly effective in a plasma channel because of a favorable phase shift that occurs in the focusing fields. Furthermore, particle-in-cell simulations show that the self-fields of the injected bunches actually tend to reduce the energy spread on the final beam. The final beam characteristics can be calculated using a computationally inexpensive Hamiltonian formulation when beam-loading effects are minimal.
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Jackson L, Ting A, McKay S, Galea P, Skeoch C. A randomised controlled trial of morphine versus phenobarbitone for neonatal abstinence syndrome. Arch Dis Child Fetal Neonatal Ed 2004; 89:F300-4. [PMID: 15210660 PMCID: PMC1721707 DOI: 10.1136/adc.2003.033555] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
BACKGROUND The incidence of neonatal abstinence syndrome (NAS) has increased 10-fold over the last decade in Glasgow. In the Princess Royal Maternity Hospital, it now accounts for 17% of special care baby unit (SCBU) admissions. OBJECTIVE To compare opiate replacement therapy (morphine sulphate) with the present standard treatment (phenobarbitone) for management of NAS. The primary study end point was duration of pharmaceutical treatment. Secondary end points were the requirement for additional drugs and the requirement for SCBU admission. DESIGN Double blind, randomised controlled clinical trial. METHODS Differential diagnoses were excluded, and two consecutive Lipsitz scores > 4 defined NAS requiring treatment. Infants were randomised to receive morphine sulphate or phenobarbitone. Treatments were identical in appearance, odour, and volume. Increments, decrements, and discontinuation of treatments were protocol driven. RESULTS Seventy five infants participated. All mothers received opiate replacement therapy (methadone) during pregnancy and most used other drugs (n = 62, 83%). No significant difference in maternal drug use patterns was observed between treatment groups. Median treatment duration was four days shorter with opiate replacement (8 v 12 days, Mann-Whitney U test, p = 0.02). Phenobarbitone treated infants tended to require second line treatment (47% v 35%, chi(2) test, p = 0.11) and SCBU admission (62% v 30%, chi(2) test, p = 0.04) more often. CONCLUSIONS Opiate replacement therapy appears to be superior for management of symptomatic NAS when maternal opiate use is prevalent. The shorter treatment duration and lower requirement for higher intensity nursing may have significant cost implications. Tailoring NAS treatment to local maternal drug use may result in similar benefits.
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Peñano JR, Sprangle P, Serafim P, Hafizi B, Ting A. Stimulated Raman scattering of intense laser pulses in air. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 68:056502. [PMID: 14682899 DOI: 10.1103/physreve.68.056502] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2003] [Indexed: 05/24/2023]
Abstract
Stimulated rotational Raman scattering (SRRS) is known to be one of the processes limiting the propagation of high-power laser beams in the atmosphere. In this paper, SRRS, Kerr nonlinearity effects, and group velocity dispersion of short laser pulses and pulse trains are analyzed and simulated. Fully time-dependent, three-dimensional, nonlinear propagation equations describing the Raman interaction, optical Kerr nonlinearity due to bound electrons, and group velocity dispersion are presented and discussed. The effective time-dependent nonlinear refractive index containing both Kerr and Raman processes is derived. Linear stability analysis is used to obtain growth rates and phase matching conditions for the SRRS, modulational, and filamentation instabilities. Numerical solutions of the propagation equations in three dimensions show the detailed evolution of the Raman scattering instability for various pulse formats. The dependence of the growth rate of SRRS on pulse duration is examined and under certain conditions it is shown that short (approximately psec) laser pulses are stable to the SRRS instability. The interaction of pulses in a train through the Raman polarization field is also illustrated.
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Abstract
AIM To design an accommodating intraocular lens with extended accommodative range that can be adapted to current standard phacoemulsification and endocapsular implantation technique. METHOD Ray tracing analysis and lens design; cadaver eye implantation. RESULTS Ray tracing analysis indicated that axial movement of an exaggerated converging anterior optic linked by spring loaded haptics to a compensatory static diverging posterior optic produced greater change in conjugation power of the eye compared to axial movement of a single optic lens. A dual optic one piece foldable silicone lens was constructed and implanted via a 4 mm corneal incision into the capsular bag of two cadaver eyes. CONCLUSION A dual optic intraocular lens design can increase the optical effect of a given displacement and suggests improvements for accommodating intraocular lenses.
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Gordon DF, Hafizi B, Hubbard RF, Peñano JR, Sprangle P, Ting A. Asymmetric self-phase modulation and compression of short laser pulses in plasma channels. PHYSICAL REVIEW LETTERS 2003; 90:215001. [PMID: 12786561 DOI: 10.1103/physrevlett.90.215001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2002] [Indexed: 05/24/2023]
Abstract
A relativistically intense femtosecond laser pulse propagating in a plasma channel undergoes dramatic photon deceleration while propagating a distance on the order of a dephasing length. The deceleration of photons is localized to the back of the pulse and is accompanied by compression and explosive growth of the ponderomotive potential. Fully explicit particle-in-cell simulations are applied to the problem and are compared with ponderomotive guiding center simulations. A numerical Wigner transform is used to examine local frequency shifts within the pulse and to suggest an experimental diagnostic of plasma waves inside a capillary.
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Peñano JR, Hafizi B, Sprangle P, Hubbard RF, Ting A. Raman forward scattering and self-modulation of laser pulses in tapered plasma channels. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 66:036402. [PMID: 12366262 DOI: 10.1103/physreve.66.036402] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2002] [Indexed: 05/23/2023]
Abstract
The propagation of intense laser pulses with durations longer than the plasma period through tapered plasma channels is investigated theoretically and numerically. General propagation equations are presented and reduced partial differential equations that separately describe the forward Raman (FR) and self-modulation (SM) instabilities in a nonuniform plasma are derived. Local dispersion relations for FR and SM instabilities are used to analyze the detuning process arising from a longitudinal density gradient. Full-scale numerical fluid simulations indicate parameters that favorably excite either the FR or SM instability. The suppression of the FR instability and the enhancement of the SM instability in a tapered channel in which the density increases longitudinally is demonstrated. For a pulse undergoing a self-modulation instability, calculations show that the phase velocity of the wakefield in an untapered channel can be significantly slower than the pulse group velocity. Simulations indicate that this wake slippage can be forestalled through the use of a tapered channel.
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Miller TL, Easley KA, Zhang W, Orav EJ, Bier DM, Luder E, Ting A, Shearer WT, Vargas JH, Lipshultz SE. Maternal and infant factors associated with failure to thrive in children with vertically transmitted human immunodeficiency virus-1 infection: the prospective, P2C2 human immunodeficiency virus multicenter study. Pediatrics 2001; 108:1287-96. [PMID: 11731650 PMCID: PMC4383837 DOI: 10.1542/peds.108.6.1287] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
OBJECTIVE Many children with human immunodeficiency virus-1 (HIV-1) have chronic problems with growth and nutrition, yet limited information is available to identify infected children at high risk for growth abnormalities. Using data from the prospective, multicenter P2C2 HIV study, we evaluated the relationships between maternal and infant clinical and laboratory factors and impaired growth in this cohort. METHODS Children of HIV-1-infected women were enrolled prenatally or within the first 28 days of life. Failure to thrive (FTT) was defined as an age- and sex-adjusted weight z score < or =-2.0 SD. Maternal baseline covariates included age, race, illicit drug use, zidovudine use, CD4+ T-cell count, and smoking. Infant baseline predictors included sex, race, CD4+ T-cell count, Centers for Disease Control stage, HIV-1 RNA, antiretroviral therapy, pneumonia, heart rate, cytomegalovirus, and Epstein-Barr virus infection status. RESULTS The study cohort included 92 HIV-1-infected and 439 uninfected children. Infected children had a lower mean gestational age, but birth weights, lengths, and head circumferences in the 2 groups were similar. Mothers of growth-delayed infants were more likely to have smoked tobacco and used illicit drugs during pregnancy. In repeated-measures analyses of weight and length or height z scores, the means of the HIV-1-infected group were significantly lower at 6 months of age (P <.001) and remained lower throughout the first 5 years of life. In a multivariable Cox regression analysis, FTT was associated with a history of pneumonia (relative risk [RR] = 8.78; 95% confidence interval [CI]: 3.59-21.44), maternal use of cocaine, crack, or heroin during pregnancy (RR = 3.17; 95% CI: 1.51-6.66), infant CD4+ T-cell count z score (RR = 2.13 per 1 SD decrease; 95% CI: 1.25-3.57), and any antiretroviral therapy by 3 months of age (RR = 2.77; 95% CI: 1.16-6.65). After adjustment for pneumonia and antiretroviral therapy, HIV-1 RNA load remained associated with FTT in the subset of children whose serum was available for viral load analysis. CONCLUSIONS Clinical and laboratory factors associated with FTT among HIV-1-infected children include history of pneumonia, maternal illicit drug use during pregnancy, lower infant CD4+ T-cell count, exposure to antiretroviral therapy by 3 months of age (non-protease inhibitor), and HIV-1 RNA viral load.
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Nagaratnam N, Ting A, Jolley D. Thalamic tumour presenting as frontal lobe dysfunction. Int J Clin Pract 2001; 55:492-3. [PMID: 11594265] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/21/2023] Open
Abstract
A 64-year-old man presented with a change in personality and behaviour but with no neurological deficits. He exhibited impaired executive functions, apathy, unsteadiness of gait and falling; he lacked insight and exhibited purposeless behaviour, making loud grunting noises. A CT scan at 6 months revealed no abnormality, but at 9 months CT and MRI showed a bilateral thalamic tumour. The presenting symptoms had similarities to frontal lobe dysfunction progressing to dementia.
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Nagaratnam N, Nagaratnam K, Jolley D, Ting A. Dementia following posterior cortical atrophy—a descriptive clinical case report. Arch Gerontol Geriatr 2001; 33:179-90. [PMID: 15374033 DOI: 10.1016/s0167-4943(01)00179-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2000] [Revised: 06/04/2001] [Accepted: 06/06/2001] [Indexed: 10/18/2022]
Abstract
Whether posterior cortical atrophy is a distinct entity or a variant of one of the other degenerative processes continues to be debated. We describe five patients four of whom had bilateral changes of posterior cortical atrophy on the CT scan. These four had a cluster of symptoms consistent with parieto-occiptial dysfunction together with a spectrum of dementia. The fifth patient with unilateral changes had optic ataxia, apraxia of gait and dementia. Three of the five patients were heavy drinkers of alcohol but any direct causal link between alcohol and posterior cortical atrophy is tenuous but alcohol could be a consideration in lowering the threshold for dementia in conjunction with other determinants. The study revealed there is little or no difficulty in recognizing posterior cortical atrophy in the early stages and the end stages are sufficiently uniform to reduce the diagnostic uncertainty.
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Sprangle P, Hafizi B, Peñano JR, Hubbard RF, Ting A, Moore CI, Gordon DF, Zigler A, Kaganovich D, Antonsen TM. Wakefield generation and GeV acceleration in tapered plasma channels. PHYSICAL REVIEW E 2001; 63:056405. [PMID: 11415017 DOI: 10.1103/physreve.63.056405] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2000] [Revised: 11/22/2000] [Indexed: 11/07/2022]
Abstract
To achieve multi-GeV electron energies in the laser wakefield accelerator (LWFA), it is necessary to propagate an intense laser pulse long distances in a plasma without disruption. One of the purposes of this paper is to evaluate the stability properties of intense laser pulses propagating extended distances (many tens of Rayleigh ranges) in plasma channels. A three-dimensional envelope equation for the laser field is derived that includes nonparaxial effects such as group velocity dispersion, as well as wakefield and relativistic nonlinearities. It is shown that in the broad beam, short pulse limit the nonlinear terms in the wave equation that lead to Raman and modulation instabilities cancel. This cancellation can result in pulse propagation over extended distances, limited only by dispersion. Since relativistic focusing is not effective for short pulses, the plasma channel provides the guiding necessary for long distance propagation. Long pulses (greater than several plasma wavelengths), on the other hand, experience substantial modification due to Raman and modulation instabilities. For both short and long pulses the seed for instability growth is inherently determined by the pulse shape and not by background noise. These results would indicate that the self-modulated LWFA is not the optimal configuration for achieving high energies. The standard LWFA, although having smaller accelerating fields, can provide acceleration for longer distances. It is shown that by increasing the plasma density as a function of distance, the phase velocity of the accelerating field behind the laser pulse can be made equal to the speed of light. Thus electron dephasing in the accelerating wakefield can be avoided and energy gain increased by spatially tapering the plasma channel. Depending on the tapering gradient, this luminous wakefield phase velocity is obtained several plasma wavelengths behind the laser pulse. Simulations of laser pulses propagating in a tapered plasma channel are presented. Experimental techniques for generating a tapered density in a capillary discharge are described and an example of a GeV channel guided standard LWFA is presented.
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Hubbard RF, Kaganovich D, Hafizi B, Moore CI, Sprangle P, Ting A, Zigler A. Simulation and design of stable channel-guided laser wakefield accelerators. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 63:036502. [PMID: 11308780 DOI: 10.1103/physreve.63.036502] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/1999] [Revised: 10/02/2000] [Indexed: 05/23/2023]
Abstract
Most laser wakefield accelerator (LWFA) experiments to date have operated in the self-modulated (SM) regime and have been self-guided. A channel-guided LWFA operating in the standard or resonant regime is expected to offer the possibility of high electron energy gain and high accelerating gradients without the instabilities and poor electron beam quality associated with the SM regime. Plasma channels such as those produced by a capillary discharge have demonstrated guiding of intense laser pulses over distances of several centimeters. Optimizing the performance in a resonant LWFA constrains the on-axis plasma density in the channel to a relatively narrow range. A scaling model is presented that quantifies resonant LFWA performance in terms of the maximum accelerating gradient, dephasing length, and dephasing-limited energy gain. These performance quantities are expressed in terms of laser and channel experimental parameters, clearly illustrating some of the tradeoffs in the choice of parameters. The predicted energy gain in this model is generally lower than that indicated by simpler scaling models. Simulations agree well with the scaling model in both low and high plasma density regimes. Simulations of a channel-guided, self-modulated LWFA are also presented. Compared with the resonant LWFA regime, the requirements on laser and channel parameters in the SM regime are easier to achieve, and a channel-guided SM-LWFA is likely to be less unstable than a self-guided SM-LWFA.
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