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Biomedical subjects

M Y Yu

Publications and source records attributed to M Y Yu.

At least 19 recordsLinked to original sources
PubMed2005

Direct acceleration of solid-density plasma bunch by ultraintense laser.

The interaction of a petawatt laser with a small solid-density plasma bunch is studied by particle-in-cell simulation. It is shown that when irradiated by a laser of intensity >10(21) W/cm2, a dense plasma bunch of micrometer size can be efficiently accelerated. The kinetic energy of the ions in the high-density region of the plasma bunch can exceed ten MeV at a density in the 10(23)-cm(-3) level. Having a flux density orders of magnitude higher than that of the traditional charged-particle pulses, the laser-accelerated plasma bunch can have a wide range of applications. In particular, such a dense energetic plasma bunch impinging on the compressed fuel in inertial fusion can significantly enhance the nuclear-reaction cross section and is thus a promising alternative for fast ignition.

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PubMed2005

Ion drag force in plasmas at high electronegativity.

The electric as well as the positive- and negative-ion drag forces on an isolated dust grain in an electronegative plasma are studied for large negative-ion densities, when the negative ions are not Boltzmann distributed. The investigation is carried out for submicrometer dust particles, so that the theory of Coulomb scattering is applicable for describing ion-dust interaction. Among the forces acting on the dust grain, the negative-ion drag force is found to be important. The effects of the negative-ion density, neutral-gas pressure, and dust-grain size on the forces are also considered. It is shown that by increasing the density of the negative ions one can effectively manipulate the dust grains. Our results imply that both dust voids and balls can be formed.

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PubMed2005

Laser-confined fusion.

An approach for producing a large quantity of neutrons is proposed. It involves compression of a fuel foil and confinement of the resulting plasma between two intense laser pulses. It is shown that two circularly polarized laser pulses of amplitude a = 7 illuminating a deuterium-tritium foil of areal density 3.3 x 10(18) cm(-2) can produce about 4.2 x 10(6) neutrons per joule of the input laser energy.

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PubMed2005

Comparison between constant feedback and limiter controllers.

Using symbolic dynamics of the one-dimensional unimodal map, the chaos stabilization mechanics of the feedback and limiter control schemes are considered. For feedback control, it is found that the control strength can be efficiently obtained from the superstable parameter of the embedded periodic orbits, and the scaling of the control-space period-doubling bifurcation cascade still obeys the Feigenbaum law. For Sarkovskii orbits, the scaling is also consistent with that of the original chaotic system. For limiter control, a single critical point in the unimodal map is extended to a superstable periodic window and a simple approach for determining the value of the control plateau is found. The scaling in the control space of the period-doubling bifurcation cascade is indeed superexponential. A different scaling for the fine structure of the Sarkovskii sequence is also found. Simple one-dimensional unimodal maps can also be used to generate maximum-length shift-register sequences.

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PubMed2004

Spatially averaged model of complex-plasma discharge with self-consistent electron energy distribution.

A global, or averaged, model for complex low-pressure argon discharge plasmas containing dust grains is presented. The model consists of particle and power balance equations taking into account power loss on the dust grains and the discharge wall. The electron energy distribution is determined by a Boltzmann equation. The effects of the dust and the external conditions, such as the input power and neutral gas pressure, on the electron energy distribution, the electron temperature, the electron and ion number densities, and the dust charge are investigated. It is found that the dust subsystem can strongly affect the stationary state of the discharge by dynamically modifying the electron energy distribution, the electron temperature, the creation and loss of the plasma particles, as well as the power deposition. In particular, the power loss to the dust grains can take up a significant portion of the input power, often even exceeding the loss to the wall.

Journal Article↗
PubMed2004

Ultrashort relativistic electromagnetic solitons.

Ultrashort high-intensity electromagnetic solitons in both underdense and overdense plasmas are investigated. Comparison is made for solitons with smooth and sharp electron density profiles. It is found that subcycle relativistic solitons can propagate from low-density to high-density plasmas.

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PubMed2004

Extended experience in the use of laparoscopic ultrasound to detect pelvic nodal metastasis in patients with cervical carcinoma.

OBJECTIVE: To evaluate the use of laparoscopic ultrasound (USG) to detect pelvic nodal metastasis in patients with early stage cervical carcinoma. METHODS: Laparoscopic USG was used to search for pelvic lymph node metastasis in stage Ia2 to IIa cervical carcinoma patients before radical hysterectomy. Suspicious lymph nodes identified by laparoscopic USG were removed laparoscopically for pathological confirmation by frozen section. If nodal metastasis was diagnosed, radical hysterectomy would be cancelled but enlarged lymph nodes were removed preferably by laparoscopic approach before closing the abdomen. These patients were treated with radiotherapy after recovering from the surgery. By comparing the laparoscopic USG and pathological findings of lymph nodes removed with or without radical hysterectomy, diagnostic accuracy of laparoscopic USG was determined. RESULTS: Ninety-three patients were recruited and the final analysis included 90 patients. Laparoscopic USG found suspicious lymph nodes in 17 patients and nodal metastases were confirmed pathologically in 14 of them. Three patients with macroscopic and five patients with microscopic pelvic nodal metastases were missed by laparoscopic USG. The accuracy, sensitivity, specificity, positive and negative predictive value of laparoscopic USG in detecting pelvic lymph node metastasis were 87.8%, 63.6%, 95.6%, 82.4%, and 89%, respectively. Macroscopic metastatic nodes were successfully removed laparoscopically in 11 out of 14 patients and laparotomy was required for the other three patients. CONCLUSIONS: Laparoscopic USG can be performed with no major morbidity. This technique is sensitive in detecting macroscopic but not microscopic metastatic pelvic lymph nodes. Removal of macroscopic metastatic nodes identified via laparoscopic USG via laparoscopic approach could be accomplished in majority of patients.

Adult↗
PubMed2003

Relativistic channeling by intense laser pulse in overdense plasmas.

Channeling in overdense plasma by relativistic laser pulse is investigated. The critical laser power needed to maintain a plasma channel as well as the mode profiles of the electromagnetic fields in the channel cross section are obtained analytically. A scaling law showing that the critical power is proportional to the square of the background plasma density is found.

Journal Article↗
PubMed2003

Optimization of ion acceleration in the interaction of intense femtosecond laser pulses with ultrathin foils.

Ion emission is investigated using particle-in-cell simulations where a Gaussian laser pulse with duration 50 fs and intensity 1.37x10(19) W/cm(2) is incident obliquely onto ultrathin solid foils. When the foil is thicker than 0.1 microm, it is opaque to the laser light and the highest ion energy drops exponentially with target thickness. Optimization of ion acceleration occurs for a target with a thickness of 0.04 microm when it becomes transparent to the laser light. The behaviors of the high-energy electrons oscillating in the charge separation potential at the front and the rear of the target, as well as the enhanced electron acceleration in the laser pulse, play dominant roles for the observed features of ion emission. The relation of the optimal target thickness with parameters of the incident laser pulse and foil targets is also discussed.

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PubMed2003

Low-pressure diffusion equilibrium of electronegative complex plasmas.

A self-consistent fluid theory of complex electronegative colloidal plasmas in parallel-plate low-pressure discharge is presented. The self-organized low-pressure diffusion equilibrium is maintained through sources and sinks of electrons, positive and negative ions, in plasmas containing dust grains. It is shown that the colloidal dust grain subsystem strongly affects the stationary state of the discharge by dynamically modifying the electron temperature and particle creation and loss processes. The model accounts for ionization, ambipolar diffusion, electron and ion collection by the dusts, electron attachment, positive-ion-negative-ion recombination, and relevant elastic and inelastic collisions. The spatial profiles of electron and positive-ion-negative-ion number densities, electron temperature, and dust charge in electronegative SiH4 discharges are obtained for different grain size, input power, neutral gas pressure, and rates of negative-ion creation and loss.

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PubMed2003

Ion-acoustic waves in a complex plasma with negative ions.

A self-consistent theory of linear waves in complex laboratory plasmas containing dust grains and negative ions is presented. A comprehensive model for such plasmas including source and sink effects associated with the presence of dust grains and negative ions is introduced. The stationary state of the plasma as well as the dispersion and damping characteristics of the waves are investigated. All relevant processes, such as ionization, diffusion, electron attachment, negative-positive ion recombination, dust charge relaxation, and dissipation due to electron and ion elastic collisions with neutrals and dust particles, as well as charging collisions with the dusts, are taken into consideration.

Journal Article↗
PubMed2003

Nonuniform non-neutral plasma in a trap.

An analytical model for breathing oscillations in a nonuniform non-neutral plasma slab is developed. The plasma is relatively small and warm with the smallest dimension only of several Debye lengths. Nonuniformity in the equilibrium results in a frequency shift associated with pressure and boundary effects. The plasma size and temperature, being related to the frequency shift, can therefore be evaluated from frequency measurements. In particular, for small nonuniform plasmas the frequency of the breathing mode is twice that predicted by the cold fluid theory. Nonlinear oscillations are also considered and the pressure is shown to have an important effect on the dynamics. Analytical solutions for linear and nonlinear oscillations are obtained and compared with that from one-dimensional particle-in-cell simulations. Good agreement is found.

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PubMed2002

High-intensity laser-field amplification between two foils.

Interaction of two oppositely directed ultraintense laser pulses with two closely placed thin foils is modeled analytically and investigated by particle-in-cell simulation. It is shown that laser energy can be trapped and accumulated between the foils. The intensity could reach a 100-fold that of the pump lasers. The trapping is found to be bistable and the parameters for stable energy confinement and enhancement are given. The ultrahigh fields that can be produced have many potential applications, including that of verifying nonlinear quantum electrodynamics effects.

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PubMed2002

Nonlinear standing waves in bounded plasmas.

An analytical model for nonlinear volume oscillations in a bounded cold plasma is developed. Although here the familiar propagating wave solutions do not exist, exact nonlinear standing waves subject to appropriate boundary conditions can nevertheless be found. The behaviors of the electrons and ions are described self-consistently in terms of Lagrangian variables. The analytical solutions are compared with that from particle-in-cell simulations. Good agreement is found in the regimes of interest.

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PubMed2002

Electron acceleration and high-order harmonic generation by an intense short pulse laser in a magnetic field.

Electron acceleration and short-wavelength radiation generation by an intense, short, linearly polarized laser pulse in an external magnetic field parallel to that of the light wave is investigated classically. It is found that enhanced electron acceleration by the laser can occur. After the pulse has passed, much of the energy gained by the electron is retained in its relativistic cyclotron motion. The electron emits radiation at high harmonics of the cyclotron frequency until the static magnetic field decays.

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PubMed2002

Expression of apoptotic regulators and their significance in cervical cancer.

Insufficient apoptosis is implicated in many human cancers, including cervical carcinoma. The objectives of this study were to explore changes of apoptosis-regulating gene expression and their clinical significance in cervical cancer. The expression of apoptosis-regulating genes, including five Bcl-2 family and two caspase family members, was evaluated in 43 cervical invasive squamous cell carcinomas, using immunohistochemistry. Specimens in which >or=10% of the neoplastic cells showed cytosolic immunoreactivity were considered to be immunopositive. Results were correlated with clinico-pathologic characteristics of the subjects. All seven apoptotic regulators examined were positive in a proportion of the tumors. The percentage of cases expressing Bax was higher in the patients without evidence of disease after treatment than in the patients alive with disease or who died of disease (P<0.05). A significant difference in disease-free survival was detected between Bax-positive and -negative groups (P<0.05), and in overall survival between Mcl-1-positive and -negative groups (P<0.05). Significant association between the seven markers tested was only found for caspase 3 and Bak immunoreactivity in cervical carcinoma (P<0.05). The results demonstrate expression of multiple apoptosis-modulating proteins in cervical cancer. There appears to be complex regulation of apoptosis protein levels in association with clinical behavior of cervical squamous cell carcinoma.

Apoptosis↗
PubMed2002

Parameters and equilibrium profiles for large-area surface-wave sustained plasmas.

The equilibrium profiles of the plasma parameters of large-area rf discharges in a finite-length metal-shielded dielectric cylinder are computed using a two-dimensional fluid code. The rf power is coupled to the plasma through edge-localized surface waves traveling in the azimuthal direction along the plasma edge. It is shown that self-consistent accounting for axial plasma diffusion and radial nonuniformity of the electron temperature can explain the frequently reported deviations of experimentally measured radial density profiles from that of the conventional linear diffusion models. The simulation results are in a good agreement with existing experimental data obtained from surface-wave sustained large-diameter plasmas.

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