Small-Scale Interstellar Na I Structure Toward M92

We have used integral field echelle spectroscopy with the DensePak fiber-optic array on the KPNO WIYN telescope to observe the central 27" x 43" of the globular cluster M92 in the Na I D wavelength region at a spatial resolution of 4". Two interstellar Na I absorption components are evident in the spectra at LSR velocities of 0 km/s (Cloud 1) and -19 km/s (Cloud 2). Substantial strength variations in both components are apparent down to scales limited by the fiber-to-fiber separations. The derived Na I column densities differ by a factor of 4 across the Cloud 1 absorption map and by a factor of 7 across the Cloud 2 map. Using distance upper limits of 400 and 800 pc for Cloud 1 and Cloud 2, respectively, the absorption maps indicate structure in the ISM down to scales of 1600 and 3200 AU. The fiber-to-fiber Na I column density differences toward M92 are comparable to those found in a similar study of the ISM toward the globular cluster M15. Overall, the structures in the interstellar components toward M92 have significantly lower column densities than those toward M15. We interpret these low column density structures as small-scale turbulent variations in the gas and compare them to the larger-scale, higher column density variations toward M15, which may be the hallmarks of actual H I structures.Comment: 9 pages, 2 figures, accepted for publication in ApJ Letter

Low-Metallicity Gas Clouds in a Galaxy Proto-Cluster at Redshift 2.38

We present high resolution spectroscopy of a QSO whose sight-line passes through the halo of a pair of elliptical galaxies at redshift 2.38. This pair of galaxies probably lies at the center of a galaxy proto-cluster, and is embedded in a luminous extended Ly-alpha nebula. The QSO sight-line intersects two small gas clouds within this halo. These clouds have properties similar to those of high velocity clouds (HVCs) seen in the halo of the Milky Way. The gas is in a cool (< 2 x 10^4 K) and at least 20% neutral phase, with metallicities in the range -3.0 < [Fe/H] < -1.1 and neutral hydrogen column densities of ~10^19.5 /cm^2. The origin of these clouds is unclear. The presence of low metallicity gas within this possible proto-cluster implies either that the intra-cluster medium has not been enriched with metals at this redshift, or the clouds are embedded within a hot, ionized, metal-rich gas phase.Comment: Accepted to appear in ApJ Letter

Voltage-controlled electron tunnelling from a single self-assembled quantum dot embedded in a two-dimensional-electron-gas-based photovoltaic cell

We perform high-resolution photocurrent (PC) spectroscopy to investigate resonantly the neutral exciton ground-state (X0) in a single InAs/GaAs self-assembled quantum dot (QD) embedded in the intrinsic region of an n-i-Schottky photodiode based on a two-dimensional electron gas (2DEG), which was formed from a Si delta-doped GaAs layer. Using such a device, a single-QD PC spectrum of X0 is measured by sweeping the bias-dependent X0 transition energy through that of a fixed narrow-bandwidth laser via the quantum-confined Stark effect (QCSE). By repeating such a measurement for a series of laser energies, a precise relationship between the X0 transition energy and bias voltage is then obtained. Taking into account power broadening of the X0 absorption peak, this allows for high-resolution measurements of the X0 homogeneous linewidth and, hence, the electron tunnelling rate. The electron tunnelling rate is measured as a function of the vertical electric field and described accurately by a theoretical model, yielding information about the electron confinement energy and QD height. We demonstrate that our devices can operate as 2DEG-based QD photovoltaic cells and conclude by proposing two optical spintronic devices that are now feasible.Comment: 34 pages, 11 figure

Revealing the Dusty Warm Absorber in MCG--6-30-15 with the Chandra HETG

We present detailed evidence for a warm absorber in the Seyfert 1 galaxy MCG--6-30-15 and dispute earlier claims for relativistic O line emission. The HETG spectra show numerous narrow, unresolved (FWHM < 200 km/s) absorption lines from a wide range of ionization states of N, O, Mg, Ne, Si, S, Ar, and Fe. The O VII edge and 1s^2--1snp resonance line series to n=9 are clearly detected at rest in the AGN frame. We attribute previous reports of an apparently highly redshifted O VII edge to the 1s^2--1snp (n > 5) O VII resonance lines, and a neutral Fe L absorption complex. The shape of the Fe L feature is nearly identical to that seen in the spectra of several X-ray binaries, and in laboratory data. The implied dust column density agrees with that obtained from reddening studies, and gives the first direct X-ray evidence for dust embedded in a warm absorber. The O VIII resonance lines and weak edge are also detected, and the spectral rollover below 2 keV is explained by the superposition of numerous absorption lines and edges. We identify, for the first time, a KLL resonance in the O VI photoabsorption cross section, giving a measure of the O VI column density. The O VII (f) emission detected at the systemic velocity implies a covering fraction of ~5% (depending on the observed vs. time-averaged ionizing flux). Our observations show that a dusty warm absorber model is not only adequate to explain all the spectral features > 0.48 keV (< 26 \AA) the data REQUIRE it. This contradicts the interpretation of Branduardi-Raymont et al. (2001) that this spectral region is dominated by highly relativistic line emission from the vicinity of the black hole.Comment: 4.5 pages, 1 color figure, accepted (April 2001) for publication in ApJL, not many changes from the initial submission - updated/added some measuements for the O VII resonance series, and added a discussion about FeO2 grain

¬MPPT pada Sistem PV Menggunakan Algoritma Firefly dan Modified P&O dengan Konverter Hybrid Cuk Terkoneksi ke Grid Satu Phasa di Bawah Kondisi Partial Shaded

— Photovoltaic (PV) merupakan sumber energi terbarukan yang paling banyak dijumpai di alam serta merupakn energi alternatif yang sangat pesat perkembangannya. Untuk mengahasilkan daya, sebuah PV dipengaruhi sebuah nilai intensitas cahaya matahari yang mengenainya. Sebuah sistem PV membutuhkan sebuah kontrol yang bertujuan untuk meningkatkan efisien daya PV tersebut. Kontrol ini adalah Maximum Power Point Tracking (MPPT) yang dapat mengoptimalkan daya yang dihasilkan oleh PV. Sebuah PV hanya menghasilkan nilai tegangan yang rendah, untuk itu perlu menggunakan koverter DC-DC step up untuk menaikan rasio tegangan DC tadi. Untuk mengoptimalkan sistem ini, diperlukan sebuah konverter yang efisien dan dapat menghasilkan rasio konversi tegangan yang tinggi. Pada penelitian menggunakan firefly algorithm (FFA) dan modified perturb and observe (P&amp;O) sebagai MPPT untuk mendapatkan nilai daya optimal pada keluaran PV. Konverter DC-DC yang digunakan adalah hybrid cuk converter boost mode yang memiliki rasio tegangan yang tinggi. Dari DC-link kemudian masuk ke inverter (VSI) yang diinterkoneksi dengan grid menggunakan current control. Hasil analisis simulasi menunjukan bahwa FFA dan P&amp;O mampu menghasilkan daya PV yang optimum dengan riak yang kecil dan konverter hybrid cuk converter boost mode dapat menghasilkan rasio tegangan yang lebih besar dibandingkan konverter cuk biasa. Kata Kunci — PV, MPPT FFA, MPPT P&amp;O, Hybrid Cuk Converter, DC-Link, Inverter Grid Connecte

Population coding by globally coupled phase oscillators

A system of globally coupled phase oscillators subject to an external input is considered as a simple model of neural circuits coding external stimulus. The information coding efficiency of the system in its asynchronous state is quantified using Fisher information. The effect of coupling and noise on the information coding efficiency in the stationary state is analyzed. The relaxation process of the system after the presentation of an external input is also studied. It is found that the information coding efficiency exhibits a large transient increase before the system relaxes to the final stationary state.Comment: 7 pages, 9 figures, revised version, new figures added, to appear in JPSJ Vol 75, No.

New Observations of the Interstellar Medium in the Lyman Break Galaxy MS 1512-cB58

We present the results of a detailed study of the interstellar medium of MS 1512-cB58, an L* Lyman break galaxy at z = 2.7276, based on new spectral observations obtained with the Echelle Spectrograph and Imager on the Keck II telescope at 58 km/s resolution. We focus in particular on the chemical abundances and kinematics of the interstellar gas and our main findings are as follows. Even at this relatively early epoch, the ISM of this galaxy is already highly enriched in elements released by Type II supernovae; the abundances of O, Mg, Si, P, and S are all about 2/5 of their solar values. In contrast, N and the Fe-peak elements Mn, Fe, and Ni are underabundant by a factor of about 3. Based on current ideas of stellar nucleosynthesis, these results can be understood if most of the metal enrichment in cB58 has taken place within the last 300 million years, the timescale for the release of N from intermediate mass stars. cB58 appears to be an example of a galaxy in the process of converting its gas into stars on a few dynamical timescales; quite possibly we are witnessing the formation of a galactic bulge or an elliptical galaxy. The energetic star formation activity has stirred the interstellar medium to high velocities of up to 1000 km/s. The net effect is a bulk outflow of the ISM at a speed of 255 km/s and at a rate which exceeds the star formation rate. It is unclear whether this gas will be lost or retained by the galaxy. We point out that the chemical and kinematic properties of cB58 are markedly different from those of most damped Lyman alpha systems at the same redshift.Comment: 38 pages, LaTeX, 9 Postscript Figures. Accepted for publication in the Astrophysical Journal. Sections 3.3 and 5.3 expanded, and two additional figures included, following referee's repor

Warm inflation model building

We review the main aspects of the warm inflation scenario, focusing on the inflationary dynamics and the predictions related to the primordial spectrum of perturbations, to be compared with the recent cosmological observations. We study in detail three different classes of inflationary models, chaotic, hybrid models and hilltop models, and discuss their embedding into supersymmetric models and the consequences for model building of the warm inflationary dynamics based on first principles calculations. Due to the extra friction term introduced in the inflaton background evolution generated by the dissipative dynamics, inflation can take place generically for smaller values of the field, and larger values of couplings and masses. When the dissipative dynamics dominates over the expansion, in the so-called strong dissipative regime, inflation proceeds with sub-planckian inflaton values. Models can be naturally embedded into a supergravity framework, with sugra corrections suppressed by the Planck mass now under control, for a larger class of K\"ahler potentials. In particular, this provides a simpler solution to the "eta" problem in supersymmetric hybrid inflation, without restricting the K\"ahler potentials compatible with inflation. For chaotic models dissipation leads to a smaller prediction for the tensor-to-scalar ratio and a less tilted spectrum when compared to the cold inflation scenario. We find in particular that a small component of dissipation renders the quartic model now consistent with the current CMB data.Comment: 22 pages, 5 figure

Thermodynamically admissible form for discrete hydrodynamics

We construct a discrete model of fluid particles according to the GENERIC formalism. The model has the form of Smoothed Particle Hydrodynamics including correct thermal fluctuations. A slight variation of the model reproduces the Dissipative Particle Dynamics model with any desired thermodynamic behavior. The resulting algorithm has the following properties: mass, momentum and energy are conserved, entropy is a non-decreasing function of time and the thermal fluctuations produce the correct Einstein distribution function at equilibrium.Comment: 4 page

The Homogeneity of Interstellar Oxygen in the Galactic Disk

We present an analysis of high resolution HST Space Telescope Imaging Spectrograph (STIS) observations of O I 1356 and H I Lyman-alpha absorption in 36 sight lines that probe a variety of Galactic disk environments and include paths that range over nearly 4 orders of magnitude in f(H_2), over 2 orders of magnitude in mean sight line density, and that extend up to 6.5 kpc in length. Consequently, we have undertaken the study of gas-phase O/H abundance ratio homogeneity using the current sample and previously published Goddard High-Resolution Spectrograph (GHRS) results. Two distinct trends are identified in the 56 sight line sample: an apparent decrease in gas-phase oxygen abundance with increasing mean sight line density and a gap between the mean O/H ratio for sight lines shorter and longer than about 800 pc. The first effect is a smooth transition between two depletion levels associated with large mean density intervals; it is centered near a density of 1.5 cm^-3 and is similar to trends evident in gas-phase abundances of other elements. Paths less dense than the central value exhibit a mean O/H ratio of log_10 (O/H) = -3.41+/-0.01 (or 390+/-10 ppm), which is consistent with averages determined for several long, low-density paths observed by STIS (Andre et al. 2003) and short low-density paths observed by FUSE (Moos et al. 2002). Sight lines of higher mean density exhibit an average O/H value of log_10 (O/H) = -3.55+/-0.02 (284+/-12 ppm). The datapoints for low-density paths are scattered more widely than those for denser sight lines, due to O/H ratios for paths shorter than 800 pc that are generally about 0.10 dex lower than the values for longer ones.Comment: 33 pages, including 8 figures and 4 tables; accepted for publication in ApJ, tentatively in Oct 200