Effects of Humidity on the Electro-Optical-Thermal Characteristics of High-Power LEDs

LEDs are subjected to environments with high moisture in many applications. In this paper, the experiments reveal photometric and colorimetric degradation at high humidity. Corresponding spectral power analysis and parameter extraction indicate that the flip-chip bonded LED samples show accelerated chip failure compared to the conventionally bonded samples. The chip-related failure induces greater heat accumulation, which correlates with the increase in heating power observed in the package. However, the temperature rise and thermal resistance for the flip-chip bonded LEDs do not increase substantially as compared to the conventionally bonded LEDs. This is because the junction temperature can be reduced with a flip-chip die-bonding configuration where the heat generated in the LED chip is dissipated effectively onto the AlN substrate, thereby reducing the increase in temperature rise and thermal resistance. The experimental results are supported by evaluation of the derivative structure functions. In addition, as the thermal resistance of the LED package varies with different humidity levels, there is a need to specify the conditions of humidity in data sheets as LED manufacturers routinely specify a universal thermal resistance value under a fixed operating condition

Reconstructing the Equation of State for Dark Energy In the Double Complex Symmetric Gravitational Theory

We propose to study the accelerating expansion of the universe in the double complex symmetric gravitational theory (DCSGT). The universe we live in is taken as the real part of the whole spacetime ${\cal M}^4_C(J)$ which is double complex. By introducing the spatially flat FRW metric, not only the double Friedmann Equations but also the two constraint conditions $p_J=0$ and $J^2=1$ are obtained. Furthermore, using parametric $D_L(z)$ ansatz, we reconstruct the $\omega^{'}(z)$ and $V(\phi)$ for dark energy from real observational data. We find that in the two cases of $J=i,p_J=0$ and $J=\epsilon,p_J\neq 0$, the corresponding equations of state $\omega^{'}(z)$ remain close to -1 at present ($z=0$) and change from below -1 to above -1. The results illustrate that the whole spacetime, i.e. the double complex spacetime ${\cal M}^4_C(J)$, may be either ordinary complex ($J=i,p_J=0$) or hyperbolic complex ($J=\epsilon,p_J\neq 0$). And the fate of the universe would be Big Rip in the future.Comment: 5 pages, 5 figures, accepted by Commun. Theor. Phy

Space-time properties of the higher twist amplitudes

A consistent and intuitive description of the twist-4 corrections to the hadron structure functions is presented in a QCD-improved parton model using time-ordered perturbative theory, where the collinear singularities are naturally eliminated. We identify the special propagators with the backward propagators of partons in time order.Comment: 18 Pages, Latex, 8 Ps figures, To appear in Phys. Rev.

Hidden symmetries for thermodynamics and emergence of relativity

Erik Verlinde recently proposed an idea about the thermodynamic origin of gravity. Though this is a beautiful idea which may resolve many long standing problems in the theories of gravity, it also raises many other problems. In this article I will comment on some of the problems of Verlinde's proposal with special emphasis on the thermodynamical origin of the principle of relativity. It is found that there is a large group of hidden symmetries of thermodynamics which contains the Poincare group of the spacetime for which space is emergent. This explains the thermodynamic origin of the principle of relativity.Comment: V1: 4 pages, comments/criticisms welcomed; V2: references added; V3: typos and minor corrections? V4? substantial changes in Section 3 and other parts mad

Neutrino-Deuteron Scattering in Effective Field Theory at Next-to-Next-to Leading Order

We study the four channels associated with neutrino-deuteron breakup reactions at next-to-next to leading order in effective field theory. We find that the total cross-section is indeed converging for neutrino energies up to 20 MeV, and thus our calculations can provide constraints on theoretical uncertainties for the Sudbury Neutrino Observatory. We stress the importance of a direct experimental measurement to high precision in at least one channel, in order to fix an axial two-body counterterm.Comment: 32 pages, 14 figures (eps

Comparison of s- and d-wave gap symmetry in nonequilibrium superconductivity

Recent application of ultrafast pump/probe optical techniques to superconductors has renewed interest in nonequilibrium superconductivity and the predictions that would be available for novel superconductors, such as the high-Tc cuprates. We have reexamined two of the classical models which have been used in the past to interpret nonequilibrium experiments with some success: the mu* model of Owen and Scalapino and the T* model of Parker. Predictions depend on pairing symmetry. For instance, the gap suppression due to excess quasiparticle density n in the mu* model, varies as n^{3/2} in d-wave as opposed to n for s-wave. Finally, we consider these models in the context of S-I-N tunneling and optical excitation experiments. While we confirm that recent pump/probe experiments in YBCO, as presently interpreted, are in conflict with d-wave pairing, we refute the further claim that they agree with s-wave.Comment: 14 pages, 11 figure

Computer simulations of hard pear-shaped particles

We report results obtained from Monte Carlo simulations investi- gating mesophase formation in two model systems of hard pear-shaped particles. The first model considered is a hard variant of the trun- cated Stone-Expansion model previously shown to form nematic and smectic mesophases when embedded within a 12-6 Gay-Berne-like po- tential [1]. When stripped of its attractive interactions, however, this system is found to lose its liquid crystalline phases. For particles of length to breadth ratio k = 3, glassy behaviour is seen at high pressures, whereas for k = 5 several bi-layer-like domains are seen, with high intradomain order but little interdomain orientational correlation. For the second model, which uses a parametric shape parameter based on the generalised Gay-Berne formalism, results are presented for particles with elongation k = 3; 4 and 5. Here, the systems with k = 3 and 4 fail to display orientationally ordered phases, but that with k = 5 shows isotropic, nematic and, unusually for a hard-particle model, interdigitated smectic A2 phases.</p

Acute Myeloid Leukemia: Focus on Novel Therapeutic Strategies

Acute myeloid leukemia (AML) is a heterogeneous disease with variable clinical outcomes. Cytogenetic analysis reveals which patients may have favorable risk disease, but 5-year survival in this category is only approximately 60%, with intermediate and poor risk groups faring far worse. Advances in our understanding of the biology of leukemia pathogenesis and prognosis have not been matched with clinical improvements. Unsatisfactory outcomes persist for the majority of patients with AML, particularly the elderly. Novel agents and treatment approaches are needed in the induction, post-remission and relapsed settings. The additions of clofarabine for relapsed or refractory disease and the hypomethylating agents represent recent advances. Clinical trials of FLT3 inhibitors have yielded disappointing results to date, with ongoing collaborations attempting to identify the optimal role for these agents. Potential leukemia stem cell targeted therapies and treatments in the setting of minimal residual disease are also under investigation. In this review, we will discuss recent advances in AML treatment and novel therapeutic strategies

Localized surface states in HTSC: Alternative mechanism of zero-bias conductance peaks

It is shown that the quasiparticle states localized in the vicinity of surface imperfections of atomic size can be responsible for the zero-bias tunneling conductance peaks in high-Tc superconductors. The contribution from these states can be easily separated from other mechanisms using their qualitatively different response on an external magnetic field.Comment: REVTeX, 4 pages, 2 figs; to be published in PR