4,491 research outputs found
Spectral studies of some hydroxy-derivatives of anthraquinones
The u.v., visible, and i.r. spectra of several hydroxy-anthraquinones are discussed and the bands are assigned. These bands are compared with those of anthracene and anthraquinone. The band at 207 nm. is assigned to a n-sigma* transition; the bands at 252, 272, and 326 nm. are assigned by measuring spectra in solvents of various polarities. The stability constant for the 12-dihydroxyanthraquinone-ethanol complex is obtained
A Robust Solution Procedure for Hyperelastic Solids with Large Boundary Deformation
Compressible Mooney-Rivlin theory has been used to model hyperelastic solids,
such as rubber and porous polymers, and more recently for the modeling of soft
tissues for biomedical tissues, undergoing large elastic deformations. We
propose a solution procedure for Lagrangian finite element discretization of a
static nonlinear compressible Mooney-Rivlin hyperelastic solid. We consider the
case in which the boundary condition is a large prescribed deformation, so that
mesh tangling becomes an obstacle for straightforward algorithms. Our solution
procedure involves a largely geometric procedure to untangle the mesh: solution
of a sequence of linear systems to obtain initial guesses for interior nodal
positions for which no element is inverted. After the mesh is untangled, we
take Newton iterations to converge to a mechanical equilibrium. The Newton
iterations are safeguarded by a line search similar to one used in
optimization. Our computational results indicate that the algorithm is up to 70
times faster than a straightforward Newton continuation procedure and is also
more robust (i.e., able to tolerate much larger deformations). For a few
extremely large deformations, the deformed mesh could only be computed through
the use of an expensive Newton continuation method while using a tight
convergence tolerance and taking very small steps.Comment: Revision of earlier version of paper. Submitted for publication in
Engineering with Computers on 9 September 2010. Accepted for publication on
20 May 2011. Published online 11 June 2011. The final publication is
available at http://www.springerlink.co
Band structure in classical field theory
Stability and instability bands in classical mechanics are well-studied in
connection with systems such as described by the Mathieu equation. We examine
whether such band structure can arise in classical field theory in the context
of an embedded kink in 1+1 dimensions. The static embedded kink is unstable to
perturbations but we show that if the kink is dynamic it can exhibit stability
in certain parameter bands. Our results are relevant for estimating the
lifetimes of various embedded defects and, in particular, loops of electroweak
Z-string.Comment: 6 pages, 4 fig. Reference added, Fig. 3 updated with improved
numerical code, minor comments added. Version to be published in Phys. Rev.
Dynamic Analysis Of A Novel Manpowered Transportation Vehicle With High Mechanical Efficiency
This paper evaluates the dynamics of a novel manpowered
transportation vehicle. The vehicle has a novel mechanism that
maximizes the mechanical input work and utilizes the weight of the
rider for propulsion. The rider applies reciprocating stepping linear
forces to drive chain and ratchet mechanism. The later transfer the
reciprocating motion into a unidirectional rotational motion at the rear
wheel to propel the vehicle. We analyzed the dynamics of the driving
and transmission mechanism and derived the equations of motion, at
first. Then, we evaluated the performance of the vehicle. Results show
significant advantages of the novel driving mechanism
Solitary wave dynamics in time-dependent potentials
We rigorously study the long time dynamics of solitary wave solutions of the
nonlinear Schr\"odinger equation in {\it time-dependent} external potentials.
To set the stage, we first establish the well-posedness of the Cauchy problem
for a generalized nonautonomous nonlinear Schr\"odinger equation. We then show
that in the {\it space-adiabatic} regime where the external potential varies
slowly in space compared to the size of the soliton, the dynamics of the center
of the soliton is described by Hamilton's equations, plus terms due to
radiation damping. We finally remark on two physical applications of our
analysis. The first is adiabatic transportation of solitons, and the second is
Mathieu instability of trapped solitons due to time-periodic perturbations.Comment: 38 pages, some typos corrected, one reference added, one remark adde
Organized Current Patterns in Disordered Conductors
We present a general theory of current deviations in straight current
carrying wires with random imperfections, which quantitatively explains the
recent observations of organized patterns of magnetic field corrugations above
micron-scale evaporated wires. These patterns originate from the most efficient
electron scattering by Fourier components of the wire imperfections with
wavefronts along the direction. We show that long range
effects of surface or bulk corrugations are suppressed for narrow wires or
wires having an electrically anisotropic resistivity
Peripartum hysterectomy for cesarean section with morbidly adherent placenta: case series of 25 patients
Background: The current paper reports the outcome of case series of patients presented with placenta accreta confirmed histopathologicaly after management by peripartum hysterectomy.Methods: The study was set in Womenâs Health Hospital, Assiut University, Egypt. This was a case series of 25 women presented with placenta accreta between May 2017 and April 2018. We included all pregnant women with placenta previa as diagnosed by ultrasound with suspicion of abnormal placentation by Doppler, confirmed intra-operatively undergoing either emergent or elective CS. All cases were performed by an expert team of obstetricians and anesthetists. Cesarean delivery was done under general anesthesia through pfannensteil incision. The primary outcome was the estimated intra-operative blood loss through assessment of amount of blood in the suction by ml, difference between the weight of surgical drapes and towels before and after operation.Results: Pre-operative Hb was 10.64±1.01 gm/dL and there was significant decline in the postoperative Hb reaching 8.36±1.21 gm/dL (p<0.001). The mean drop in Hb was 2.28±1.43gm/dL. Estimated intra-operative blood loss was 974.4±398.05 ml in the towels and 847.6±362.56 ml in the suction apparatus. The total blood loss was 1822±653.73 ml. The mean number of units of whole blood transfused was 2160.0±825.6 ml and fresh frozen plasma was 1010.0±349.7 ml. Regarding intra-operative complications, bladder injury was the most common one in 14 cases (56%), followed by ureteric injury in two cases (8%). Postoperative ICU admission was in 6 cases (24%) and the mean duration of hospital stay 12.44 ± 4.07 days. No cases of maternal mortality.Conclusions: In conclusion, peripartum hysterectomy is considered life-saving surgery in patients with placenta accreta
- âŠ