Maintenance, Repair, and Overhaul Performance Indicators for Military Aircraft

Modern day military and commercial aircraft systems are an integration of a large number of sub-systems and components. Each of these systems has different reliability characteristics and different probability distributions governing their failure rates. Space constraints and structural layout of the aircraft govern the position of each component. The accessibility, reliability, and snag diagnostic-ability determines the maintainability of the aircraft. The peculiarities involved in aircraft maintenance are discussed and performance measurement indices for O, I and D level maintenance are presented in this paper. These performance measurement indices are intended for use by aircraft maintenance managers for instituting process improvements for achieving best flight and maintenance safety records, improve operational availability of the aircraft and reduce costs.Defence Science Journal, 2012, 62(2), pp.83-89, DOI:http://dx.doi.org/10.14429/dsj.62.88

Star formation in galaxies at z~4-5 from the SMUVS survey: a clear starburst/main-sequence bimodality for Halpha emitters on the SFR-M* plane

We study a large galaxy sample from the Spitzer Matching Survey of the UltraVISTA ultra-deep Stripes (SMUVS) to search for sources with enhanced 3.6 micron fluxes indicative of strong Halpha emission at z=3.9-4.9. We find that the percentage of "Halpha excess" sources reaches 37-40% for galaxies with stellar masses log10(M*/Msun) ~ 9-10, and decreases to <20% at log10(M*/Msun) ~ 10.7. At higher stellar masses, however, the trend reverses, although this is likely due to AGN contamination. We derive star formation rates (SFR) and specific SFR (sSFR) from the inferred Halpha equivalent widths (EW) of our "Halpha excess" galaxies. We show, for the first time, that the "Halpha excess" galaxies clearly have a bimodal distribution on the SFR-M* plane: they lie on the main sequence of star formation (with log10(sSFR/yr^{-1})<-8.05) or in a starburst cloud (with log10(sSFR/yr^{-1}) >-7.60). The latter contains ~15% of all the objects in our sample and accounts for >50% of the cosmic SFR density at z=3.9-4.9, for which we derive a robust lower limit of 0.066 Msun yr^{-1} Mpc^{-3}. Finally, we identify an unusual >50sigma overdensity of z=3.9-4.9 galaxies within a 0.20 x 0.20 sq. arcmin region. We conclude that the SMUVS unique combination of area and depth at mid-IR wavelengths provides an unprecedented level of statistics and dynamic range which are fundamental to reveal new aspects of galaxy evolution in the young Universe.Comment: 18 pages, 11 figures, 1 table. Re-submitted to the ApJ, after addressing referee report. Main changes with respect to v1: a new section and a new appendix have been added to investigate further the origin and robustness of the sSFR bimodality. No conclusion change

Imaging features of rare mesenychmal liver tumours: beyond haemangiomas.

Tumours arising from mesenchymal tissue components such as vascular, fibrous and adipose tissue can manifest in the liver. Although histopathology is often necessary for definitive diagnosis, many of these lesions exhibit characteristic imaging features. The radiologist plays an important role in suggesting the diagnosis, which can direct appropriate immunohistochemical staining at histology. The aim of this review is to present clinical and imaging findings of a spectrum of mesenchymal liver tumours such as haemangioma, epithelioid haemangioendothelioma, lipoma, PEComa, angiosarcoma, inflammatory myofibroblastic tumour, solitary fibrous tumour, leiomyoma, leiomyosarcoma, Kaposi sarcoma, mesenchymal hamartoma, undifferentiated embryonal sarcoma, rhabdomyosarcoma and hepatic metastases. Knowledge of the characteristic features of these tumours will aid in guiding the radiologic diagnosis and appropriate patient management

Electronic excitations and the tunneling spectra of metallic nanograins

Tunneling-induced electronic excitations in a metallic nanograin are classified in terms of {\em generations}: subspaces of excitations containing a specific number of electron-hole pairs. This yields a hierarchy of populated excited states of the nanograin that strongly depends on (a) the available electronic energy levels; and (b) the ratio between the electronic relaxation rate within the nano-grain and the bottleneck rate for tunneling transitions. To study the response of the electronic energy level structure of the nanograin to the excitations, and its signature in the tunneling spectrum, we propose a microscopic mean-field theory. Two main features emerge when considering an Al nanograin coated with Al oxide: (i) The electronic energy response fluctuates strongly in the presence of disorder, from level to level and excitation to excitation. Such fluctuations produce a dramatic sample dependence of the tunneling spectra. On the other hand, for excitations that are energetically accessible at low applied bias voltages, the magnitude of the response, reflected in the renormalization of the single-electron energy levels, is smaller than the average spacing between energy levels. (ii) If the tunneling and electronic relaxation time scales are such as to admit a significant non-equilibrium population of the excited nanoparticle states, it should be possible to realize much higher spectral densities of resonances than have been observed to date in such devices. These resonances arise from tunneling into ground-state and excited electronic energy levels, as well as from charge fluctuations present during tunneling.Comment: Submitted to the Physical Review

Solving rate equations for electron tunneling via discrete quantum states

We consider the form of the current-voltage curves generated when tunneling spectroscopy is used to measure the energies of individual electronic energy levels in nanometer-scale systems. We point out that the voltage positions of the tunneling resonances can undergo temperature-dependent shifts, leading to errors in spectroscopic measurements that are proportional to temperature. We do this by solving the set of rate equations that can be used to describe electron tunneling via discrete quantum states, for a number of cases important for comparison to experiments, including (1) when just one spin-degenerate level is accessible for transport, (2) when 2 spin-degenerate levels are accessible, with no variation in electron-electron interactions between eigenstates, and (3) when 2 spin-degenerate levels are accessible, but with variations in electron-electron interactions. We also comment on the general case with an arbitrary number of accessible levels. In each case we analyze the voltage-positions, amplitudes, and widths of the current steps due to the quantum states.Comment: REVTeX 4, 10 pages, 12 figures, submitted to Phys. Rev. B. Associated programs available at http://www.ccmr.cornell.edu/~ralph

A Model for Ferromagnetic Nanograins with Discrete Electronic States

We propose a simple phenomenological model for an ultrasmall ferromagnetic grain, formulated in terms of the grain's discrete energy levels. We compare the model's predictions with recent measurements of the discrete tunneling spectrum through such a grain. The model can qualitatively account for the observed features if we assume (i) that the anisotropy energy varies among different eigenstates of one grain, and (ii) that nonequilibrium spin accumulation occurs.Comment: 4 pages, 2 figure

Hydrogen peroxide and lime based oxidative pretreatment of wood waste to enhance enzymatic hydrolysis for a biorefinery: Process parameters optimization using response surface methodology

Response surface methodology (RSM) was adopted for the optimization of process variables in the alkaline peroxide oxidation (APO) pretreatment of Vitellaria paradoxa sawdust based on central composite design (CCD) experiments. A 23 five level CCD with central and axial points was used to develop a statistical model for the optimization of process variables. Maximum response for the pretreatment was obtained when applying the optimum values for temperature (150 �C), time (45 min), and 1% (v/v) H2O2. At the optimum conditions, up to 70% of the initial hemicellulose was removed in treatments, which also caused some delignification (up to 11% of the initial lignin was removed), whereas cellulose was almost quantitatively retained in the solid phase. Alkaline peroxide assisted wet air oxidation (APAWAO) pretreatment at the optimum conditions resulted in enrichment up to 60% cellulose content along with solubilization of 80% hemicellulose and 17% of lignin initially present in the raw sawdust. Reducing sugars yield after 72 h enzymatic hydrolysis of pretreated biomass at optimized APO conditions was 177.89 mg equivalent glucose g�1 dry biomass. Addition of 10 bar air pressure at the optimized pretreatment conditions increased the sugars yield to 263.49 mg equivalent glucose g�1 dry biomass

The Spitzer Matching Survey of the UltraVISTA Ultra-deep Stripes (SMUVS):The Evolution of Dusty and Nondusty Galaxies with Stellar Mass at z = 2–6

The Spitzer Matching Survey of the UltraVISTA Ultra-deep Stripes (SMUVS) has obtained the largest ultradeep Spitzer maps to date in a single field of the sky. We considered the sample of about 66,000 SMUVS sources at z = 2–6 to investigate the evolution of dusty and nondusty galaxies with stellar mass through the analysis of the galaxy stellar mass function (GSMF), extending previous analyses about one decade in stellar mass and up to z = 6. We further divide our nondusty galaxy sample with rest-frame optical colors to isolate red quiescent (“passive”) galaxies. At each redshift, we identify a characteristic stellar mass in the GSMF above which dusty galaxies dominate, or are at least as important as nondusty galaxies. Below that stellar mass, nondusty galaxies compose about 80% of all sources, at all redshifts except at z = 4–5. The percentage of dusty galaxies at z = 4–5 is unusually high: 30%–40% for {M}* ={10}9{--}{10}10.5 {M}ȯ and &gt;80% at M * &gt; 1011 M ⊙, which indicates that dust obscuration is of major importance in this cosmic period. The overall percentage of massive ({log}}10({M}* /{M}ȯ )&gt; 10.6) galaxies that are quiescent increases with decreasing redshift, reaching &gt;30% at z ∼ 2. Instead, the quiescent percentage among intermediate-mass galaxies (with {log}}10({M}* /{M}ȯ )=9.7{--}10.6) stays roughly constant at a ∼10% level. Our results indicate that massive and intermediate-mass galaxies clearly have different evolutionary paths in the young universe and are consistent with the scenario of galaxy downsizing

Nonequilibrium excitations in Ferromagnetic Nanoparticles

In recent measurements of tunneling transport through individual ferromagnetic Co nanograins, Deshmukh, Gu\'eron, Ralph et al. \cite{mandar,gueron} (DGR) observed a tunneling spectrum with discrete resonances, whose spacing was much smaller than what one would expect from naive independent-electron estimates. In a previous publication, \cite{prl_kleff} we had suggested that this was a consequence of nonequilibrium excitations, and had proposed a ``minimal model'' for ferromagnetism in nanograins with a discrete excitation spectrum as a framework for analyzing the experimental data. In the present paper, we provide a detailed analysis of the properties of this model: We delineate which many-body electron states must be considered when constructing the tunneling spectrum, discuss various nonequilibrium scenarios and compare their results with the experimental data of Refs. \cite{mandar,gueron}. We show that a combination of nonequilibrium spin- and single-particle excitations can account for most of the observed features, in particular the abundance of resonances, the resonance spacing and the absence of Zeeman splitting.Comment: 13 pages, 10 figure