Niobate-on-Niobate Resonators with Aluminum Electrodes

In this work, we have successfully engineered and examined suspended laterally vibrating resonators (LVRs) on a lithium niobate thin film on lithium niobate carrier wafer (LN-on-LN) platform, powered by aluminum interdigital transducers (IDTs). Unlike the lithium niobate-on-silicon system, the LN-on-LN platform delivers a stress-neutral lithium niobate thin film exhibiting the quality of bulk single crystal. The creation of these aluminum-IDTs-driven LN-on-LN resonators was achieved utilizing cutting-edge vapor-HF release techniques. Our testing revealed both symmetric (S0) and sheer horizontal (SH0) lateral vibrations in the LVR resonators. The resonators displayed a quality factor (Q) ranging between 500 and 2600, and coupling coefficient $k_{eff}^2$ up to 13.9%. The figure of merit (FOM) $k_{eff}^2 \times Q$ can reach as high as 294. The yield of these devices proved to be impressively reliable. Remarkably, our LN-on-LN devices demonstrated a consistently stable temperature coefficient of frequency (TCF) and good power handling. Given the low thermal conductivity of lithium niobate, our LN-on-LN technology presents promising potential for future applications such as highly sensitive uncooled sensors using monolithic chip integrated resonator arrays

Traversable wormholes in bi-metric gravity

The ghost-free bi-metric gravity theory is a viable theory of gravity that explores the interaction between a massless and a massive graviton and can be described in terms of two dynamical metrics. In this paper, we present an exact static, spherically symmetric vacuum solution within this theory. The solution is spatially Schwarzschild-de Sitter, with the value of the cosmological constant determined by the graviton mass and the interaction parameters of the theory. Notably, for specific parameter ranges, the solution represents a traversable Lorentzian wormhole that violates the weak energy condition near its throat. Furthermore, we have investigated the evolution of scalar and electromagnetic fields in this wormhole spacetime and observed the presence of arbitrarily long-lived quasi-resonant modes in the quasinormal spectrum.Comment: 14 pages, 7 figure

Self-Guidance and Self-Focusing of Rippled Electromagnetic Radiation Pulse in High Density Magnetoactive Plasma

Inside the plasma, when an intense rippled electromagnetic radiation pulse experiences self-focusing, one need to taking account of radial expansion in view of charge displacement due to ponderomotive force on electron and variation in the mass of oscillating electron under the influence of relativistic effect due to electromagnetic field. The extraordinary-mode (E-mode) propagation in a magnetoactive plasma, with stationary magnetic field, which is analogous to the wavering magnetic field of the electromagnetic radiation pulse, is the key feature for the self-guided propagation of rippling electromagnetic radiation pulse in magnetoactive plasma. If the condition for ultra-fast volume ionization is achieved, the radiation pulse itself can generate such a stationary magnetic field. It is demonstrated that external magnetic field affects the channels, causing them to bend. These effects cast new light on the phenomena of self-focusing of rippled electromagnetic radiation pulse. They raise the possibility of combining energy from several channels into one. It is found that the magnetic field strongly influences the plasma dynamic behavior and overall propagation of rippled electromagnetic radiation pulse. Keywords: Self-focusing, Self-guidance, Magnetized-plasma, Beam-propagation, Nonlinearit

A Note on Low-Dimensional String Compactifications

We study supersymmetric compactifications of type II strings on eightfolds to two dimensions. It is demonstrated that the type IIB string on an eightfold is free of gravitational anomalies. T-duality requires that this theory when further compactified on a circle must have a vacuum momentum; this is explicitly shown to be present and to have the right value. A subtlety in the relation of IIB compactifications and M-Theory orientifolds to two dimensions is pointed out.Comment: 12 pages Tex file, no figure

Gravitational Couplings and Z2Z_2 Orientifolds

The interplay between gravitational couplings on branes and the occurrence of fractional flux in low dimensional orientifolds is examined. It is argued that gravitational couplings need to be assigned not only to D-branes but also to orientifold planes. The fractional charges of the orientifold $d$-planes can be understood in terms of flux quantization of the $d-3$ form potential and modified Bianchi identities. Detailed results are presented for the case of the type IIB orientifold on $T^6/Z_2$, which is dual to F-theory on a complex 4-fold with terminal singularities.Comment: 24 pages, harvmac,Numerical coefficients of R^4 couplings have been corrected, and are now in agreement with recent results of hep-th/9812071 and hep-th/9812088. No other changes. This revision supercedes the published version of this pape

Atomic force microscopy: a powerful tool for high-resolution imaging of spermatozoa

Atomic force microscopy (AFM) has emerged as the only technique capable of real-time imaging of the surface of a living cell at nano-resolution. Since AFM provides the advantage of directly observing living biological cells in their native environment, this technique has found many applications in pharmacology, biotechnology, microbiology, structural and molecular biology, genetics and other biology-related fields. AFM has also proved to be a valuable tool for reproductive biologists. An exhaustive review on the various applications of AFM to sperm cells is presented. AFM has been extensively applied for determining the structural and topological features of spermatozoa. Unstained, unfixed spermatozoa in their natural physiological surroundings can be imaged by this technique which provides valuable information about the morphological and pathological defects in sperm cells as three-dimensional images with precise topographical details. Sperm head defects and the acrosome at the tip of the head responsible for fertilization, can be examined and correlated with the lack of functional integrity of the cell. Considerable amount of work is reported on the structural details of the highly condensed chromatin in sperm head using AFM. Detailed information on 3D topographical images of spermatozoa acquired by AFM is expected to provide a better understanding of various reproductive pathways which, in turn, can facilitate improved infertility management and/or contraceptive development

Orbifold and Orientifold Compactifications of F-Theory and M-Theory to Six and Four Dimensions

We study orbifold compactifications of F-theory which lead to $N=1$ supersymmetry in 6 and 4 spacetime dimensions. These are dual to specific orientifolds of M-theory, and in many cases to orientifolds of type IIB string theory. The equivalences are demonstrated by mapping the orbifolding transformations in the F, M and string theories to each other using dualities. We observe that M and F-theory appear to possess a property similar to discrete torsion in string theory. This is related to an ambiguity recently noted by Polchinski in the orientifold projection for 6-dimensional models. The 4-dimensional compactifications exhibit similar features, from which we predict the existence of certain new orientifolds of type IIB. Some orbifolds with higher supersymmetry are also examined.Comment: Harvmac, 30 pages (big). Additional argument relating orientifolding ambiguity to discrete torsion inserted near the end of Sec. 6, a few clarifying remarks and one reference adde