Staircase Profile Research Articles

Modelling of titanium indiffused lithium niobate channel waveguide bends: a matrix approach

An analytical model for computation of bending loss of Ti:LiNbO 3 channel waveguide bends has been presented. The analytical steps involved are as follows. The 2D refractive index profile over the cross-section of Ti:LiNbO 3 waveguide is first transformed to 1D effective-index profile along the lateral direction. A conformal mapping technique is then used to transform the effective-index profile of the waveguide bend to that of an equivalent straight waveguide. A stair-case type step-index profile is generated from the equivalent effective-index profile in lateral direction by partitioning the latter into a large number of thin sections of varying refractive indices. The overall transfer matrix of the step-index layered structure so obtained may be computed by the progressive multiplication of individual 2×2 transfer matrices relating the field components in adjacent layers. The excitation efficiency of the wave in the guiding layer shows a resonance peak around the mode propagation constant. The full-width-half-maximum (FWHM) of this peak determines the power attenuation coefficient of the bent waveguide. The losses due to the discontinuity of the curvature are also computed. The computed results for different bends including S-bends are in good agreement with the published experimental data. The computation using the model is quite fast and versatile to consider arbitrary waveguide dimensions, Ti-film thickness, diffusion parameters and wavelength of light for both TE and TM polarizations. The model, in principle, is not limited to Ti:LiNbO 3 channel waveguides only but is valid for any arbitrary graded-index channel waveguide bends provided that the refractive index profile and the wavelength dependence of the refractive index are known.

Relaxation dynamics in dense binary colloidal mixtures: Brownian dynamics simulations

Brownian dynamics simulations have been carried out on a binary colloidal mixture of particles of two different diameters interacting via a Derjaguin-Landau-Verway-Overbeek potential. As the screening length is increased a transition from liquid to crystal (at a volume fraction $\ensuremath{\varphi}=0.2$) or a glassy state (at $\ensuremath{\varphi}=0.3$) is observed. Below a certain effective temperature ${T}^{\ensuremath{\star}}$, the temporal evolution of the mean-squared displacements shows a marked subdiffusive behavior at intermediate and long times. The supercooled liquid with $\ensuremath{\varphi}=0.3$ shows a staircase profile indicating strongly cooperative jump motion which is corroborated by the behavior of van Hove self-correlation functions and the non-Gaussian parameter. The van Hove distinct correlation function, in the $\ensuremath{\beta}$ relaxation regime, shows a factorization property in accordance with the mode-coupling theory predictions. The most interesting result is the observation of cooperative hop and subsequent hop-back motion at temperatures close to the glass transition.

Evaluation of cross-linked amylose press-coated tablets for sustained drug delivery

Based on the physico-chemical properties of cross-linked amylose (CLA), a hydrophilic polymer, we were able to design dry-coated tablets for time-independent and complex drug release. To make the cores, CLA was mixed with the model drug in different proportions and then compressed. The cores were coated manually, consisting of either pure CLA or a mixture of CLA with a small proportion of solute. Diltiazem HCl and acetaminophen were the model drugs used. CLA dry-coated tablets behave as reservoir systems where the outer gel layer acts as a solution-diffusion membrane, through which transport occurs by a process of dissolution of the permeating drug in the polymer at one interface and diffusion down a gradient in thermodynamic activity. After the drug has established a uniform concentration gradient within the outer membrane (lag time), drug release is linear for the range of constant thermodynamic activity in the core. For the same core composition, decreasing the coating thickness or incorporating small amounts of NaCl in the shell shorten the release lag time and increase the release rate. By varying the drug to CLA ratio in the core we are able to optimize the release profiles. Zero-order release profiles with or without a time delay were developed. Tablets for complex delivery (staircase profile) were also devised.

Radiative transfer in a clumpy universe: The colors of high-redshift galaxies

We assess the effects of the stochastic attenuation produced by intervening QSO absorption systems on the broadband colors of galaxies at cosmological distances. We compute the H I opacity of a clumpy universe as a function of redshift, including scattering in resonant lines, such as Lyman alpha, Lyman beta, Lyman gamma, and higher order members, and Lyman-continuum absorption. Both the numerous, optically thin Lyman-alpha forest clouds and the rarer, optically thick Lyman limit systems are found to contribute to the obscuration of background sources. We study the mean properties of primeval galaxies at high redshift in four broad optical passbands, U(sub n), B, G, and R. Even if young galaxies radiated a significant amount of ionizing photons, the attenuation due to the accumulated photoelectric opacity along the path is so severe that sources beyond z approximately 3 will drop out of the U(sub n) image together. We also show that the observed B-R color of distant galaxies can be much redder than expected from a stellar population. At z approximately 3.5, the blanketing by discrete absorption lines in the Lyman series is so effective that background galaxies appear, on average, 1 mag fainter in B. By z approximately 4, the observed B magnitude increment due to intergalactic absorption exceeds 2 mag. By modeling the intrinsic UV spectral energy distribution of star-forming galaxies with a stellar population synthesis code, we show that the (B-R)(sub AB) approximately 0 criterion for identifying 'flat-spectrum,' metal-producing galaxies is biased against objects at z greater than 3. The continuum blanketing from the Lyman series produces a characteristic staircase profile in the transmitted power. We suggest that this cosmic Lyman decrement might be used as a tool to identify high-z galaxies.

New binary sequences with perfect staircase profile of linear complexity

An open problem proposed by M. Morrii and M. Kasahara is solved by a few new binary sequences with perfect staircase profile of linear complexity. Moreover, the PSP sequence with the smallest density is found.

Salivary total protein and experimental Coriolis sickness.

Symptomatic reporting has been used in quantifying the severity of motion sickness including Coriolis sickness. This study was designed to objectively examine if the dynamic changes of salivary protein concentration relate to the severity of Coriolis sickness. Healthy adults with normal vestibular function underwent a modified Coriolis Sickness Susceptibility Index (CSSI) test, utilizing a staircase profile. Salivary samples were obtained prior to stimulation, 15, 30, and 45 min following stimulus onset, and/or upon reaching "nausea-II" endpoint. Total protein concentration tended to rise over the initial 30 min of stimulation, and then level off or decline. A statistically significant difference was found between the pre-stimulation and 30 min samples. Although some variability existed among the subjects, the general pattern of changes along the time course was similar. An inverse correlation approaching statistical significance was found between control (non-stimulus) total protein levels, and minutes of Coriolis stimulation required to reach the "nausea-II" endpoint. Thus, baseline salivary total protein levels can be of use in predicting susceptibility of Coriolis sickness and other forms of motion sickness.

Perfect staircase profile of linear complexity for finite sequences

One of the most interesting themes in cryptology is the generating of the highly unpredictable pseudo-random sequences. Unfortunately, it is difficult even to define what the highly unpredictable pseudo-random sequences are. However, some measures for the unpredictability, or equivalently the randomness, of finite sequences were proposed. The linear complexity is one of such measures. We present new classes of sequences with the interesting growth property of linear complexity.

Sodium concentration in saliva along the time course of experimental Coriolis sickness.

Procedures designed to evaluate the severity of motion sickness have included subjective reporting of changes in salivation. In order to increase objectivity, we studied the sodium concentration of saliva, which is directly related to the flow rate. Healthy adults with normal vestibular function underwent a modified Coriolis Sickness Susceptibility Index (CSSI) test, utilizing a staircase profile. Saliva was collected without interrupting the stimulus by means of cotton placed beneath the subject's tongue for one minute. Samples were obtained 5 min prior to stimulation, 30 and 45 min following stimulus onset, and/or upon reaching the "nausea II" endpoint. Saliva for analysis by atomic absorption spectrophotometry was obtained by centrifugation of the cotton. A significant difference in sodium concentration was found between the baseline and 30-min sample (p less than 0.01). Although the amount of salivation was rather variable, the pattern of changes in sodium concentration was similar in all experimental cases.

Sensory-synaptic interactions in crayfish stretch receptor neurones

1. This communication describes, in the tonic stretch receptor organ (RM1) of crayfish, the inhibitory fibre's influence upon sensory modulated discharges. Periodic trapezoidal length changes were imposed, and rate plots of the afferent discharges were compared without inhibition (C) and with inhibition, either irregular (P) or regular (R), and at different rates. 2. Inhibition changed all sensory response components. Changes were dependent on issues as inhibitory rates and patterns, RM 1 discharge modulations, and pre-post-synaptic rate ratios. The most common effect was rate reduction, usually non-uniform along the cycle and with little evidence of proportionality. Saturation, i.e., inefficacy of shifts around extreme inhibitory rates was apparent. Rate increases occurred also. Accelerations were manifest by increased phasic lengthening response slopes and heights, by “faster inhibitor-faster inhibited” relations, or by postinhibitory rebounds. 3. Irregular inhibitory discharges (i) favoured variability along individual and average cycles, (ii) favoured monotonicity, (iii) rarely silenced the RM 1, and (iv) reduced without eliminating nonproportionality and saturation. 4. Regular inhibitory discharges showed the most clear-cut nonmonotonicities and saturations silencing the RM 1 effectively. Furthermore, they included characteristic epochs where (i) the RM 1 spike slid across the invariant interinhibition intervals, (ii) intervals recurred in stereotyped sequences and (iii) rate ratios had special values (e.g., 1:1, 1:2). Thus, the gradually decaying slope of the control adaptation after the lengthening transient was changed into a staircase profile or a sudden drop to a constant plateau. 5. Inhibition changed phasic and tonic sensitivities, usually refucing them (phasic decreasing less than tonic); increases, joint or individual, occurred also. The fidelity with which the rate plot reproduced the sensory stimulus was modified in many ways (e.g., by conversion into a phasic prototype, or into a system with perfect reproduction, etc.). Changes depended on the inhibitory discharge, and on the stimulus features. 6. These experiments have implications in two fields. In that of synaptic rate effects, (i) they confirm that the inhibition repertory includes slowings (predominant here) and accelerations, plus special effects, and (ii) they demonstrate extensively their dependence on the post-synaptic features. In the field of sensory control, they note sensory-synaptic interactions that, in intact animals, must arise but whose characteristics and roles can only be conjectured about.

Modal characteristics of a doubly clad step-index optical fibre: a general analytical approach

Using a fairly rigorous approach, a general characteristic equation for a doubly clad step-index fibre has been derived under the assumption that the refractive-index difference between the inner and outer cladding is small. Two different profiles, i.e., the W profile and the staircase profile, have been treated together and a discussion of their common characteristics has been made. Cutoff conditions for low-order modes have been obtained. For a certain range of values of the transverse-phase parameter ratio, the singly-clad fibre has greater mode cutoff V numbers than those of a doubly clad fibre. The analysis anticipates the possibility of obtaining greater cutoff V numbers for W-profile fibres.