The effects of temperature on different laser transitions of neodymium orthovanadate crystal

The temperature dependence of Nd:YVO4 laser crystal pumped by laser diode emitting at 808 nm is studied within the range of 5 °C to 60 °C. The spectroscopy properties of quasi three level at 914 nm (4F3/2 -4I9/2) and four level at 1064 nm (4F3/2 -4I11/2) are characterized. The lineshape function of the transition lines were broadened as the temperature increases. The phenomenon is attributed to change in linewidth, lineshift and intensity. The linewidths for both laser transition of 914 nm and 1064 nm increases with temperature with the rate of 0.105 cm-1/°C and 0.074 cm-1/°C respectively. The peak of 914nm and 1064 nm lineshapes shifted to a longer wavelength with the rate of 3.0 pm/°C and 4.2 pm/°C respectively which correspond to same amount of lineshift. The lineshape broadening with respect to the temperature is due to one-phonon emission and Raman phonon scattering processes. The intensities of 914 nm and 1064 nm transition lines are found to be decreased at the rate of 0.15 %/°C and 0.45 %/°C respectively due to non-radiative effects. Quasi three level laser transition is more temperature dependent because it terminal level is close to the ground state which suffers from higher phonon-ion interaction rather than four level laser system

ANTAGONIST MUSCLE ACTIVITY DURING MAXIMAL ISOMETRIC KNEE STRENGTH TESTING

Atrophy and weakness are common after anterior cruciate ligament injury and in people with knee osteoarthritis (Lewek et al., 2004; Williams et al., 2005). Strength testing is an important part of managing people with knee conditions such as these, as the strength is often used as a criteria for surgical timing, rehabilitation progression, and return to sport. Antagonist activity may lead to measurement errors in strength testing, which adversely impact clinical decision-making. The purpose of this study was to assess the magnitude and variability (by side and across sessions) of antagonist muscle activity during maximal voluntary isometric knee strength testing in males and females

The effect of Mach number on unstable disturbances in shock/boundary-layer interactions

The effect of Mach number on the growth of unstable disturbances in a boundary layer undergoing a strong interaction with an impinging oblique shock wave is studied by direct numerical simulation and linear stability theory (LST). To reduce the number of independent parameters, test cases are arranged so that both the interaction location Reynolds number (based on the distance from the plate leading edge to the shock impingement location for a corresponding inviscid flow) and the separation bubble length Reynolds number are held fixed. Small-amplitude disturbances are introduced via both white-noise and harmonic forcing and, after verification that the disturbances are convective in nature, linear growth rates are extracted from the simulations for comparison with parallel flow LST and solutions of the parabolized stability equations (PSE). At Mach 2.0, the oblique modes are dominant and consistent results are obtained from simulation and theory. At Mach 4.5 and Mach 6.85, the linear Navier-Stokes results show large reductions in disturbance energy at the point where the shock impinges on the top of the separated shear layer. The most unstable second mode has only weak growth over the bubble region, which instead shows significant growth of streamwise structures. The two higher Mach number cases are not well predicted by parallel flow LST, which gives frequencies and spanwise wave numbers that are significantly different from the simulations. The PSE approach leads to good qualitative predictions of the dominant frequency and wavenumber at Mach 2.0 and 4.5, but suffers from reduced accuracy in the region immediately after the shock impingement. Three-dimensional Navier-Stokes simulations are used to demonstrate that at finite amplitudes the flow structures undergo a nonlinear breakdown to turbulence. This breakdown is enhanced when the oblique-mode disturbances are supplemented with unstable Mack modes

Near-linear Time Algorithm for Approximate Minimum Degree Spanning Trees

Given a graph $G = (V, E)$, we wish to compute a spanning tree whose maximum vertex degree, i.e. tree degree, is as small as possible. Computing the exact optimal solution is known to be NP-hard, since it generalizes the Hamiltonian path problem. For the approximation version of this problem, a $\tilde{O}(mn)$ time algorithm that computes a spanning tree of degree at most $\Delta^* +1$ is previously known [F\"urer \& Raghavachari 1994]; here $\Delta^*$ denotes the minimum tree degree of all the spanning trees. In this paper we give the first near-linear time approximation algorithm for this problem. Specifically speaking, we propose an $\tilde{O}(\frac{1}{\epsilon^7}m)$ time algorithm that computes a spanning tree with tree degree $(1+\epsilon)\Delta^* + O(\frac{1}{\epsilon^2}\log n)$ for any constant $\epsilon \in (0,\frac{1}{6})$. Thus, when $\Delta^*=\omega(\log n)$, we can achieve approximate solutions with constant approximate ratio arbitrarily close to 1 in near-linear time.Comment: 17 page

Catalysis study for space shuttle vehicle thermal protection systems

Experimental results on the problem of reducing aerodynamic heating on space shuttle orbiter surfaces are presented. Data include: (1) development of a laboratory flow reactor technique for measuring gamma sub O and gamma sub N on candidate materials at surfaces, T sub w, in the nominal range 1000 to 2000, (2) measurements of gamma sub O and gamma sub N above 1000 K for both the glass coating of a reusable surface insulation material and the siliconized surface of a reinforced pyrolyzed plastic material, (3) measurement of the ablation behavior of the coated RPP material at T sub w is greater than or equal to 2150 K, (4) X-ray photoelectron spectral studies of the chemical constituents on these surfaces before and after dissociated gas exposure, (5) scanning electron micrograph examination of as-received and reacted specimens, and (6) development and exploitation of a method of predicting the aerodynamic heating consquences of these gamma sub O(T sub w) and gamma sub N(T sub w) measurements for critical locations on a radiation cooled orbiter vehicle

Molecular and thermal studies of carbon fiber precursor polymers with low thermal-oxidative stabilization characteristics

In this investigation, terpolymers, copolymers, and homopolymer of acrylonitrile with dimethylaminopropyl acrylamide (DMAPA), itaconic acid (IA) viz., poly(acrylonitrile‐ran‐3‐dimethylaminopropyl acrylamide‐ran‐itaconic acid) [P(AN‐DMAPP‐IA)], poly(acrylonitrile‐co‐3, dimethylaminopropyl acrylamide) [P(AN‐DMAPP)] were synthesized with varying amounts of comonomers using solution polymerization process. The chemical structure, composition, bonding network were determined employing infrared, 1H and, 13‐carbon nuclear magnetic resonance spectroscopic techniques. Molecular characteristics of as‐synthesized polymers such as different kinds of average molecular weights, molecular weight distribution were estimated applying solution viscometry and size exclusion chromatography. The influence of comonomers (DMPAA, IA) on the thermal stabilization characteristics of acrylonitrile terpolymers in comparison with copolymers and homopolymers of acrylonitrile were studied using differential scanning calorimetry (DSC), hyphenated thermal techniques (thermal gravimetry coupled with differential thermal analyzer).The DSC curves of P(AN‐DMAPP‐IA) exhibit a distinct broader bimodal peaks with thermal exotherm initiating at as low as 165 °C, and followed by two peaks with temperature difference of 42 °C, releasing the evolved heat at a release rate of 0.7–0.11 J g−1s−1over 10 min as compared to 1.2, 7.5 J g−1s−1 in 4.5, 2 min as observed in P(AN‐DMAPP), polyacrylonitrile, respectively. The thermal stability of P(AN‐DMAPP‐IA) and P(AN‐DMAPP), as evidenced by TGA‐DTA was found to be higher than PAN homopolymers. Specific heat capacity measurements confirmed the DSC results. Bulk densities of P(AN‐DMAPP‐IA) were in the range 0.31–0.35 g/cc. These results confirm the low‐temperature stabilization characteristics and suitability of P(AN‐DMAPP‐IA) as low cost carbon fiber precursor polymer

SENSORIMOTOR CONTROL OF THE KNEE IN MALE AND FEMALE ATHLETES

Evidence suggests that the female predisposition to knee injuries may be related to sensorimotor control (Hewett et al., 2005). The purpose of this study was to compare the quadriceps and hamstrings muscle control strategies of male and female athletes using an established method of testing muscle control (Williams et al., 2003)

Laser tattoo removal comparison between 1064 and 532 NM of a Q-switched ND:YAG laser treatment

Invention of the Q-switch advanced laser method is the most effective methods of tattoo removal compared to other methods of i.e. chemical, mechanical and surgical. In this study, we are reporting black pigment tattoo removal by comparing two wavelengths 532 nm and 1064 nm of Q-switched Nd-YAG laser. Using a single-pulse laser at 1064 nm wavelength, the maximum laser fluence for skin damage is 3.04 J/cm2 with pulse energy 0.55 J. While, at 532 nm wavelength, maximum laser fluence is 0.5 J/cm2 with pulse energy 0.42 J at 8-10 ns for tattooed skins. Moreover, after 1064 nm and 532 nm laser irradiations, skin biopsy of black tattooed rat’s skin demonstrates the ink granules local redistribution. Microscopic study indicates that black ink particles become smaller and vanished from the skins after 1064 nm laser treatment. The findings of this study indicate that 1064 nm wavelengths of Q-switched Nd-YAG laser treatment with 0.55 J pulse energy, is one of the significant methods of black tattoo removal with remarkable differences

Kinetics of Decomposition of Nitramine Propellant by Differential Scanning Calorimetry

The paper describes an experimental procedure for the determination of overall kinetic parameters for the exothermic decomposition reaction of nitramine propellant. The kinetic parameters can be obtained through the use of differential thermal analysis (DTA), differential scanning calorimetry (DSC) or thermogravimetric analysis (TGA) methods. The procedure is applicable to reactions whose behaviour can be described by the Arrhenius equation and the general rate law. In the present work, DSC technique has been used for the evaluation of Arrehenius activation parameters and specific rate constants for thermal decomposition of a typical nitramine propellant. The kinetic parameters were computed by Ozawa and Kissinger methods for comparison. The activation energy value obtained from the Ozawa method is refined by an iteration procedure using Doyle approximation for the Arrhenius temperature integral p(x)