98 research outputs found
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Determination of topological charges of polychromatic optical vortices
No full textWe introduce a simple, single beam method for determination
of the topological charge of polychromatic optical vortices. It is based on
astigmatic transformation of singular optical beams, where the intensity
pattern of a vortex beam acquires a form of dark stripes in the focal plane
of a cylindrical lens. The number of the dark stripes is equal to the modulus
of the vortex topological charge, while the stripe tilt indicates the charge
sign. We demonstrate experimentally the effectiveness of this technique by
revealing complex topological structure of polychromatic singular beams
Simultaneous phase matching and internal interference of two second-order nonlinear parametric processes
No full textWe demonstrate the simultaneous generation and internal
interference of two second-order parametric processes in a single nonlinear
quadratic crystal. The two-frequency doubling processes are Type 0 (two
extraordinary fundamental waves generate an extraordinary secondharmonic
wave) and Type I (two ordinary fundamental waves generate an
extraordinary second-harmonic wave) parametric interactions. The phasematching
conditions for both processes are satisfied in a single periodically
poled grating in LiNbO3 using quasi-phase-matching (QPM) vectors with
different orders. We observe an interference of two processes, and compare
the results with the theoretical analysis. We suggest several applications of
this effect such as polarization-independent frequency doubling and a
method for stabilizing the level of the generated second-harmonic signal
Time dependence of phase variables in a steady shear flow algorithm
No full textWe study the periodic time dependence of shear stress that occurs in a low- and a high-density fluid in a molecular dynamics algorithm for simulation of constant shear flow. We present a generalization of the linear response theory for a case when the equilibrium relaxation function and the equilibrium shear stress depend on strain. The predictions of this generalization reveal that the time dependence at low densities is a completely nonlinear effect. At high densities the amplitude of equilibrium oscillations of shear stress with strain is modified by strain-dependent viscosity, causing a decrease in amplitude proportional to shear rate in the linear response regime
Solution structure of Domains IVa and V of the τ subunit of Escherichia coli DNA polymerase III and interaction with the α subunit
No full textThe solution structure of the C-terminal Domain V of the τ subunit of E. coli DNA polymerase III was determined by nuclear magnetic resonance (NMR) spectroscopy. The fold is unique to τ subunits. Amino acid sequence conservation is pronounced for hydrophobic residues that form the structural core of the protein, indicating that the fold is representative for τ subunits from a wide range of different bacteria. The interaction between the polymerase subunits τ and α was studied by NMR experiments where α was incubated with full-length C-terminal domain (τC16), and domains shortened at the C-terminus by 11 and 18 residues, respectively. The only interacting residues were found in the C-terminal 30-residue segment of τ, most of which is structurally disordered in free τC16. Since the N- and C-termini of the structured core of τC16 are located close to each other, this limits the possible distance between α and the pentameric δτ2γδ' clamp–loader complex and, hence, between the two α subunits involved in leading- and lagging-strand DNA synthesis. Analysis of an N-terminally extended construct (τC22) showed that τC14 presents the only part of Domains IVa and V of τ which comprises a globular fold in the absence of other interaction partners
Mastectomy or breast conserving surgery? Factors affecting type of surgical treatment for breast cancer - a classification tree approach
No full textBACKGROUND:
A critical choice facing breast cancer patients is which surgical treatment – mastectomy or breast conserving surgery (BCS) – is most appropriate. Several studies have investigated factors that impact the type of surgery chosen, identifying features such as place of residence, age at diagnosis, tumor size, socio-economic and racial/ethnic elements as relevant. Such assessment of "propensity" is important in understanding issues such as a reported under-utilisation of BCS among women for whom such treatment was not contraindicated. Using Western Australian (WA) data, we further examine the factors associated with the type of surgical treatment for breast cancer using a classification tree approach. This approach deals naturally with complicated interactions between factors, and so allows flexible and interpretable models for treatment choice to be built that add to the current understanding of this complex decision process.
METHODS:
Data was extracted from the WA Cancer Registry on women diagnosed with breast cancer in WA from 1990 to 2000. Subjects' treatment preferences were predicted from covariates using both classification trees and logistic regression.
RESULTS:
Tumor size was the primary determinant of patient choice, subjects with tumors smaller than 20 mm in diameter preferring BCS. For subjects with tumors greater than 20 mm in diameter factors such as patient age, nodal status, and tumor histology become relevant as predictors of patient choice.
CONCLUSION:
Classification trees perform as well as logistic regression for predicting patient choice, but are much easier to interpret for clinical use. The selected tree can inform clinicians' advice to patients
Time-dependent response theory and nonequilibrium free-energy relations
No full textThe mathematics of time-dependent nonlinear response theory frequently leads to results which although formally exact, are not amenable to experimental application or even to use in computer simulations. Here we give a rigorous derivation of a tractable expression for the thermostatted nonlinear response of classical many body systems to time-dependent dissipative fields. The theory also allows for the concurrent parametric transformation of the system Hamiltonian. Our analysis shows once again the intimate relationship between nonequilibrium free-energy relations such as the Jarzynski equality and nonlinear response theory. We make a few remarks concerning the maximum entropy production approximation
Boron carbide nanowires with uniform CNx coatings
No full textBoron carbide nanowires with uniform carbon nitride coating layers
were synthesized on a silicon substrate using a simple thermal process. The
structure and morphology of the as-synthesized nanowires were characterized
using x-ray diffraction, scanning and transmission electron microscopy and
electron energy loss spectroscopy.A correlation between the surface smoothness
of the nanowire sidewalls and their lateral sizes has been observed and it is
a consequence of the anisotropic formation of the coating layers. A growth
mechanism is also proposed for these growth phenomena
Health impacts of pesticide exposure in a cohort of outdoor workers
No full textWe compared mortality of 1,999 outdoor staff working as part of an insecticide application program during 1935-1996 with that of 1,984 outdoor workers not occupationally exposed to insecticides, and with the Australian population. Surviving subjects also completed a morbidity questionnaire. Mortality was significantly higher in both exposed and control subjects compared with the Australian population. The major cause was mortality from smoking-related diseases. Mortality was also significantly increased in exposed subjects for a number of conditions that do not appear to be the result of smoking patterns. Compared with the general Australian population, mortality over the total study period was increased for asthma [standardized mortality ratio (SMR) = 3.45 ; 95% confidence interval (CI) , 1.39-7.10] and for diabetes (SMR = 3.57 ; 95% CI, 1.16-8.32 for subjects working < 5 years) . Mortality from pancreatic cancer was more frequent in subjects exposed to 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (SMR = 5.27 ; 95% CI, 1.09-15.40 for subjects working < 3 years) . Compared with the control population, mortality from leukemia was increased in subjects working with more modern chemicals (standardized incidence ratio = 20.90 ; 95% CI, 1.54-284.41 for myeloid leukemia in the highest exposure group) . There was also an increase in self-reported chronic illness and asthma, and lower neuropsychologic functioning scores among surviving exposed subjects when compared with controls. Diabetes was reported more commonly by subjects reporting occupational use of herbicides. These findings lend weight to other studies suggesting an association between adverse health effects and exposure to pesticides
Light bullets and dynamic pattern formation in nonlinear dissipative systems
No full textIn the search for suitable new media for the propagation of (3+1)
D optical light bullets, we show that nonlinear dissipation provides
interesting possibilities. Using the complex cubic-quintic Ginzburg-Landau
equation model with localized initial conditions, we are able to observe
stable light bullet propagation or higher-order transverse pattern formation.
The type of evolution depends on the model parameters
Achieving peak brightness in an atom laser
No full textIn this Letter we present experimental results and a simple analytic theory on the first continuous (long
pulse) Raman atom laser. We analyze the flux and brightness of a generic two state atom laser with an
analytic model that shows excellent agreement with our experiments. We show that, for the same source
size, the brightness achievable with a Raman atom laser is at least 3 orders of magnitude greater than
achievable in any other demonstrated continuously outcoupled atom laser