Charge response function and a novel plasmon mode in graphene

Polarizability of non-interacting 2D Dirac electrons has a 1/\sqrt{qv-\omega} singularity at the boundary of electron-hole excitations. The screening of this singularity by long-range electron-electron interactions is usually treated within the random phase approximation. The latter is exact only in the limit of N -> infinity, where N is the ``color'' degeneracy. We find that the ladder-type vertex corrections become crucial close to the threshold as the ratio of the n-th order ladder term to the same order RPA contribution is (\ln|qv-\omega|)^n/N^n$. We perform analytical summation of the infinite series of ladder diagrams which describe excitonic effect. Beyond the threshold, qv>\omega, the real part of the polarization operator is found to be positive leading to the appearance of a strong and narrow plasmon resonance.Comment: 4 pages, 3 figures,typos correcte

Near-infrared spectroscopy of 20 new Chandra sources in the Norma Arm

We report on CTIO/NEWFIRM and CTIO/OSIRIS photometric and spectroscopic observations of 20 new X-ray (0.5-10 keV) emitters discovered in the Norma Arm Region Chandra Survey (NARCS). NEWFIRM photometry was obtained to pinpoint the near-infrared counterparts of NARCS sources, while OSIRIS spectroscopy was used to help identify 20 sources with possible high mass X-ray binary properties. We find that (1) two sources are WN8 Wolf-Rayet stars, maybe in colliding wind binaries, part of the massive star cluster Mercer 81; (2) two are emission-line stars, possibly in X-ray binaries, that exhibit near- and mid-infrared excesses either due to free-free emission from the decretion discs of Be stars or warm dust in the stellar winds of peculiar massive stars such as B[e] supergiants or luminous blue variables; (3) one is a B8-A3 IV-V star that could be in a quiescent high mass X-ray binary system; (4) two are cataclysmic variables including one intermediate polar; (5) three may be neutron star symbiotic binaries; (6) five are most likely white dwarf symbiotic binaries; and (7) five exhibit properties more consistent with isolated giant/dwarf stars. The possible detection of one to three high mass X-ray binaries is in good agreement with our predictions. However, our study illustrates the difficulty of clearly differentiating quiescent or intermediate X-ray luminosity systems from isolated massive stars, which may lead to an underestimation of the number of known high mass X-ray binaries.Comment: 17 pages, 14 figures, 7 tables. Accepted for publication in A&

Identifikasi Dan Aplikasi Pengenalan Spektrum Bunyi Gamelan Menggunakan Jaringan Syaraf Tiruan Pada Matlab

Gamelan merupakan salah satu alat musik tradisional dari pulau Jawa. Seperangkat gamelan terdiri dari berbagai macam alat musik yang dimainkan secara bersama-sama. Karena perpaduan antara bunyi gamelan satu dengan bunyi gamelan yang lainnya menggambarkan keselaraasan dalam kehidupan bermasyarakat. Namun seiring berjalannya waktu, peminat gamelan semakin sedikit dan orang pembuat gamelan juga semakin sulit dijumpai.Gamelan yang digunakan dalam penelitian ini yaitu: Gong, Kempul, Kenong dan Bonang Penerus. Bunyi gamelan akan diidentifikasi dengan caramencari frekuensi-frekuensi bunyi gamelannya. Dengan menggunakan metode Fast Fourier Transform (FFT) suatu bunyi yang berdomain waktu dapat diubah menjadi domain frekuensi dengan salah satu software Matlab.Proses dalam jaringan syaraf tiruan Backpropagation ini menggunakan jumlah neuron yang bervariasi, diantaranya: 70, 80, 90, 100 dan 110 untuk mengetahui keakuratan jaringan dalam mengenali data yang diujikan. Hanya jumlah neuron 110 lah yang dapat mengenali data pengujian sebesar 99% untuk data pengujian pelatihan dengan MSE 0.0001233 pada epoch ke 1000. Maka hasil dalam penelitian ini jaringan dapat mengenali data pengujian dengan benar. Sehingga mengidentifikasi spektrum bunyi menggunakan jaringan syaraf tiruan dapat digunakan untuk mengenali berbagai bunyi gamelan bahkan bunyi yang lainnya

A First Look at the X-ray Population of the Young Massive Cluster VVV CL077

Multi-wavelength analysis of the young massive cluster VVV CL077 is presented for the first time. Our Chandra survey of this region enabled the detection of three X-ray emitting stellar members of the cluster, as well as a possible diffuse X-ray component that extends a few arcseconds from the cluster core with an intrinsic flux of (9+/-3)x10^-14 erg cm^-2 s^-1 in the 0.5-10 keV band. Infrared spectra we obtained for two of these X-ray point sources show absorption lines typical of the atmospheres of massive O stars. The X-ray spectrum from the visible extent of VVV CL077 i.e., a 15"-radius around the cluster, can be modeled with an absorbed power law with nH = (6+/-4)x10^22 cm^-2 and gamma = 2+/-1. In addition, the X-ray core of VVV CL077 coincides with diffuse emission seen in the infrared band and with a local maximum in the radio continuum map. A possible association with a neighboring H II region would place VVV CL077 at a distance of around 11 kpc; on the far side of the Norma Arm. At this distance, the cluster is 0.8 pc wide with a mass density of (1-4)x10^3 Msol pc^-3.Comment: accepted for publication in The Astrophysical Journal: 9 pages, 5 figure

Optical Conductivity of a Two-Dimensional Electron Liquid with Spin-Orbit Interaction

The interplay of electron-electron interactions and spin-orbit coupling leads to a new contribution to the homogeneous optical conductivity of the electron liquid. The latter is known to be insensitive to many-body effects for a conventional electron system with parabolic dispersion. The parabolic spectrum has its origin in the Galilean invariance which is broken by spin-orbit coupling. This opens up a possibility for the optical conductivity to probe electron-electron interactions. We analyze the interplay of interactions and spin-orbit coupling and obtain optical conductivity beyond RPA.Comment: 5 pages, 3 figures; final version, fig. 3 added, minor change

Many-body diagrammatic expansion in a Kohn-Sham basis: implications for Time-Dependent Density Functional Theory of excited states

We formulate diagrammatic rules for many-body perturbation theory which uses Kohn-Sham (KS) Green's functions as basic propagators. The diagram technique allows to study the properties of the dynamic nonlocal exchange-correlation (xc) kernel $f_{xc}$. We show that the spatial non-locality of $f_{xc}$ is strongly frequency-dependent. In particular, in extended systems the non-locality range diverges at the excitation energies. This divergency is related to the discontinuity of the xc potential.Comment: 4 RevTeX pages including 3 eps figures, submitted to Phys. Rev. Lett; revised version with new reference

The Norma Arm Region Chandra Survey: X-ray Populations in the Spiral Arms

We present a catalog of 1415 X-ray sources identified in the Norma arm region Chandra survey (NARCS), which covers a 2 deg x 0.8 deg region in the direction of the Norma spiral arm to a depth of $\approx$20 ks. Of these sources, 1130 are point-like sources detected with $\geq3\sigma$ confidence in at least one of three energy bands (0.5-10, 0.5-2, and 2-10 keV), five have extended emission, and the remainder are detected at low significance. Since most sources have too few counts to permit individual classification, they are divided into five spectral groups defined by their quantile properties. We analyze stacked spectra of X-ray sources within each group, in conjunction with their fluxes, variability, and infrared counterparts, to identify the dominant populations in our survey. We find that $\sim$50% of our sources are foreground sources located within 1-2 kpc, which is consistent with expectations from previous surveys. Approximately 20% of sources are likely located in the proximity of the Scutum-Crux and near Norma arm, while 30% are more distant, in the proximity of the far Norma arm or beyond. We argue that a mixture of magnetic and nonmagnetic CVs dominates the Scutum-Crux and near Norma arms, while intermediate polars (IPs) and high-mass stars (isolated or in binaries) dominate the far Norma arm. We also present the cumulative number count distribution for sources in our survey that are detected in the hard energy band. A population of very hard sources in the vicinity of the far Norma arm and active galactic nuclei dominate the hard X-ray emission down to $f_X\approx10^{-14}$ erg cm$^{-2}$ s$^{-1}$, but the distribution curve flattens at fainter fluxes. We find good agreement between the observed distribution and predictions based on other surveys.Comment: 27 pages, 19 figures, 12 tables, catalog will be made available in published ApJ version and by personal reques

Synchronization in Complex Systems Following the Decision Based Queuing Process: The Rhythmic Applause as a Test Case

Living communities can be considered as complex systems, thus a fertile ground for studies related to their statistics and dynamics. In this study we revisit the case of the rhythmic applause by utilizing the model proposed by V\'azquez et al. [A. V\'azquez et al., Phys. Rev. E 73, 036127 (2006)] augmented with two contradicted {\it driving forces}, namely: {\it Individuality} and {\it Companionship}. To that extend, after performing computer simulations with a large number of oscillators we propose an explanation on the following open questions (a) why synchronization occurs suddenly, and b) why synchronization is observed when the clapping period ($T_c$) is $1.5 \cdot T_s < T_c < 2.0 \cdot T_s$ ($T_s$ is the mean self period of the spectators) and is lost after a time. Moreover, based on the model, a weak preferential attachment principle is proposed which can produce complex networks obeying power law in the distribution of number edges per node with exponent greater than 3.Comment: 16 pages, 5 figure

Manajemen Pengembangan Pariwisata Kabupaten Semarang Di Dinas Pemuda, Olahraga, Kebudayaan, Dan Pariwisata Kabupaten Semarang

Berdasarkan potensi yang dimiliki, Kabupaten Semarang mempunyai prospek yang cukup menjanjikan untuk meningkatkan daya saing daerah baik di tingkat regional maupun nasional, khususnya beberapa komoditas yang memiliki keunggulan kompetitif pada sektor pariwisata, namun hingga saat ini belum dikembangkan secara optimal, hal ini menunjukkan bahwa upaya dari Dinas Pemuda, Olahraga, Kebudayaan dan Pariwisata Kabupaten Semarang Kabupaten Semarang belum maksimal. Sebagai gambaran banyaknya pendapatan dari sektor pariwisata Kabupaten Semarang pada semester pertama tahun 2012 telah mencapai 55 persen atau Rp 1,4 miliar dari total target sebesar Rp 2,5 miliar. Pencapaian tersebut lebih baik dibandingkan realisasi tahun 2011 yang hanya mencapai 70 persen atau 1,8 miliar dari target sebesar Rp 2,3 miliar.Namun kesuksesan Dinas Pemuda, Olahraga, Kebudayaan dan Pariwisata Kabupaten Semarang dalam meraup pendapatan bukanlah satu-satunya tolok ukur suatu keberhasilan dalam pengembangan pariwisata, melainkan proses manajerial yang sempurna dan kompeten lah yang menjadi tolak ukur keberhasilan.Hasil penelitian yang menggunakan metode deskriptif kualitatif menunjukkan bahwa manajemen pengembangan pariwisata di Dinas Pemuda, Olahraga, Kebudayaan dan Pariwisata Kabupaten Semarang belum sempurna. Hal ini dikarenakan masih adanya permasalahan di perencanaan anggaran dan pengorganisasasian dimana kurangnya pegawai berlatar belakang pendidikan pariwisata serta pembagian beban tugas yang diterima para pegawai masih kurang proporsional hal ini disebabkan karena banyaknya beban tugas tetapi tidak ditunjang dengan banyaknya personil..Saran dari hasil penelitian ini adalah untuk perencanan anggaran agar terus mengupayakan pengajuan anggaran ke segala pihak terutama pemerintah provinsi dan pusat untuk pengembangan pariwisata. Untuk pengorganisasian pegawai diberikan diklat khusus atau seminar tentang kepariwisataan dan beasiswa pariwisata untuk pegawai berprestasi serta mengupayakan usulan pemenuhan Sumber Daya Manusia melalui Badan Kepegawaian Daerah (BKD)