Instantaneous ionization rate as a functional derivative

We describe an approach defining instantaneous ionization rate (IIR) as a functional derivative of the total ionization probability. The definition is based on physical quantities which are directly measurable, such as the total ionization probability and the waveform of the pulse. The definition is, therefore, unambiguous and does not suffer from gauge non-invariance. We compute IIR by solving numerically the time-dependent Schrodinger equation for the hydrogen atom in a strong laser field. We find that the IIR lags behind the electric field, but this lag is entirely due to the long tail effect of the Coulomb field. In agreement with the previous results using attoclock methodology, therefore, the IIR we define does not show measurable delay in strong field tunnel ionization

Sub-100-as timing jitter optical pulse trains from mode-locked Er-fiber lasers

We demonstrate sub-100-attosecond timing jitter optical pulse trains generated from free-running, 77.6-MHz repetition-rate, mode-locked Er-fiber lasers. At -0.002(\pm0.001) ps2 net cavity dispersion, the rms timing jitter is 70 as (224 as) integrated from 10 kHz (1 kHz) to 38.8 MHz offset frequency, when measured by a 24-as-resolution balanced optical cross-correlator. To our knowledge, this result corresponds to the lowest rms timing jitter measured from any mode-locked fiber lasers so far. The measured result also agrees fairly well with the Namiki-Haus analytic model of quantum-limited timing jitter in stretched-pulse fiber lasers.Comment: 4 pages, 2 figures, to appear in Optics Letter

Vav1 inhibits RANKL-induced osteoclast differentiation and bone resorption

Vav1 is a Rho/Rac guanine nucleotide exchange factor primarily expressed in hematopoietic cells. In this study, we investigated the potential role of Vav1 in osteoclast (OC) differentiation by comparing the ability of bone marrow mononuclear cells (BMMCs) obtained from Vav1-deficient (Vav1−/−) and wild-type (WT) mice to differentiate into mature OCs upon stimulation with macrophage colony stimulating factor and receptor activator of nuclear kappa B ligand in vitro. Our results suggested that Vav1 deficiency promoted the differentiation of BMMCs into OCs, as indicated by the increased expression of tartrate-resistant acid phosphatase, cathepsin K, and calcitonin receptor. Therefore, Vav1 may play a negative role in OC differentiation. This hypothesis was supported by the observation of more OCs in the femurs of Vav1−/− mice than in WT mice. Furthermore, the bone status of Vav1−/− mice was analyzed in situ and the femurs of Vav1−/− mice appeared abnormal, with poor bone density and fewer number of trabeculae. In addition, Vav1-deficient OCs showed stronger adhesion to vitronectin, an αvβ3 integrin ligand important in bone resorption. Thus, Vav1 may inhibit OC differentiation and protect against bone resorption

Copper nanofiber-networked cobalt oxide composites for high performance Li-ion batteries

We prepared a composite electrode structure consisting of copper nanofiber-networked cobalt oxide (CuNFs@CoOx). The copper nanofibers (CuNFs) were fabricated on a substrate with formation of a network structure, which may have potential for improving electron percolation and retarding film deformation during the discharging/charging process over the electroactive cobalt oxide. Compared to bare CoOxthin-film (CoOxTF) electrodes, the CuNFs@CoOxelectrodes exhibited a significant enhancement of rate performance by at least six-fold at an input current density of 3C-rate. Such enhanced Li-ion storage performance may be associated with modified electrode structure at the nanoscale, improved charge transfer, and facile stress relaxation from the embedded CuNF network. Consequently, the CuNFs@CoOxcomposite structure demonstrated here can be used as a promising high-performance electrode for Li-ion batteries