The Mass-Metallicity and Luminosity-Metallicity Relation from DEEP2 at z ~ 0.8

We present the mass-metallicity (MZ) and luminosity-metallicity (LZ) relations at z ~ 0.8 from ~1350 galaxies in the Deep Extragalactic Evolutionary Probe 2 (DEEP2) survey. We determine stellar masses by fitting the spectral energy distribution inferred from photometry with current stellar population synthesis models. This work raises the number of galaxies with metallicities at z ~ 0.8 by more than an order of magnitude. We investigate the evolution in the MZ and LZ relations in comparison with local MZ and LZ relations determined in a consistent manner using ~21,000 galaxies in the Sloan Digital Sky Survey. We show that high stellar mass galaxies (log(M/M_solar)~10.6) at z ~ 0.8 have attained the chemical enrichment seen in the local universe, while lower stellar mass galaxies (log(M/M_solar)~9.2) at z ~ 0.8 have lower metallicities (Delta log(O/H)~0.15 dex) than galaxies at the same stellar mass in the local universe. We find that the LZ relation evolves in both metallicity and B-band luminosity between z ~ 0.8 and z~ 0, with the B-band luminosity evolving as a function of stellar mass. We emphasize that the B-band luminosity should not be used as a proxy for stellar mass in chemical evolution studies of star-forming galaxies. Our study shows that both the metallicity evolution and the B-band luminosity evolution for emission-line galaxies between the epochs are a function of stellar mass, consistent with the cosmic downsizing scenario of galaxy evolution.Comment: Accepted Version: 18 pages, 13 figure

Charging induced asymmetry in molecular conductors

We investigate the origin of asymmetry in various measured current-voltage (I-V) characteristics of molecules with no inherent spatial asymmetry, with particular focus on a recent break junction measurement. We argue that such asymmetry arises due to unequal coupling with the contacts and a consequent difference in charging effects, which can only be captured in a self-consistent model for molecular conduction. The direction of the asymmetry depends on the sign of the majority carriers in the molecule. For conduction through highest occupied molecular orbitals (i.e. HOMO or p-type conduction), the current is smaller for positive voltage on the stronger contact, while for conduction through lowest unoccupied molecular orbitals (i.e. LUMO or n-type conduction), the sense of the asymmetry is reversed. Within an extended Huckel description of the molecular chemistry and the contact microstructure (with two adjustable parameters, the position of the Fermi energy and the sulphur-gold bond length), an appropriate description of Poisson's equation, and a self-consistently coupled non-equilibrium Green's function (NEGF) description of transport, we achieve good agreement between theoretical and experimental I-V characteristics, both in shape as well as overall magnitude.Comment: length of the paper has been extended (4 pages to 6 pages), two new figures have been added (3 figures to 5 figures), has been accepted for PR

Current-voltage characteristics in donor-acceptor systems: Implications of a spatially varying electric field

We have studied the transport properties of a molecular device composed of donor and acceptor moieties between two electrodes on either side. The device is considered to be one-dimensional with different on-site energies and the non-equilibrium properties are calculated using Landauer's formalism. The current-voltage characteristics is found to be asymmetric with a sharp Negative Differential Resistance at a critical bias on one side and very small current on the other side. The NDR arises primarily due to the bias driven electronic structure change from one kind of insulating phase to another through a highly delocalized conducting phase. Our model can be considered to be the simplest to explain the experimental current-voltage characteristics observed in many molecular devices.Comment: 5 pages, 4 figures (accepted for publication in Physical Review B

Thermoelectric properties of Bi2Te3 atomic quintuple thin films

Motivated by recent experimental realizations of quintuple atomic layer films of Bi2Te3,the thermoelectric figure of merit, ZT, of the quintuple layer is calculated and found to increase by a factor of 10 (ZT = 7.2) compared to that of the bulk at room temperature. The large enhancement in ZT results from the change in the distribution of the valence band density of modes brought about by the quantum confinement in the thin film. The theoretical model uses ab initio electronic structure calculations (VASP) with full quantum-mechanical structure relaxation combined with a Landauer formalism for the linear-response transport coefficients.Comment: 4 figures, submitted to AP

Negative differential resistance in bilayer graphene nanoribbons

Lack of a bandgap is one of the significant challenges for application of graphene as the active element of an electronic device. A bandgap can be induced in bilayer graphene by application of a potential difference between the two layers. The simplest geometry for creating such a potential difference is two overlayed graphene nanoribbons independently contacted. Calculations, based on density functional theory and the nonequilibrium Green's function formalism, show that transmission through such a structure is a strong function of applied bias. The simulated current voltage characteristics mimic the characteristics of resonant tunneling diode featuring negative differential resistance. © 2011 American Institute of Physics.published_or_final_versio

Multi-state current switching by voltage controlled coupling of crossed graphene nanoribbons

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Variasi Spasio-temporal Jenis Makanan Ikan Motan, Thynnichthys Polylepis Di Rawa Banjiran Sungai Kampar Kiri, Riau [Spatio-temporal Variation in the Diet of Thynnichtys Polylepis in Floodplain River of Kampar Kiri, Riau]

The research aimed to describe diet composition of Thynnichthyes polylepis. The diet compositions of population from two sites (Mentulik and Simalinyang) in floodplain river of Kampar Kiri, were compared according to the month. Fishes were captured using experimental gillnet and trap. For food habits analysis, the index of preponderance method was used. The collections were performed monthly from July to December 2008, where the stomach contents of 479 specimens were assessed. Prey items of T. polylepis were basically composed of phytoplankton and zooplankton, especially Cocconeis, Nitzschia, Navicula, Cyclotella, Pleurotaenium, and Testudinella. At site Mentulik, the most common items were Cocconeis, Nitzschia, and Navicula. Conversely, at site Simalinyang, Cocconeis, Pleurotaenium, and Nitzschia more representative. In general, main food of fish origin showed the highest index values at Mentulik, whereas at Simalinyang. The composition of items varied monthly, especially at Simalinyang. Food habits of fish may be flexible according to resource availability in spatial and temporal variation

Synthesis, Characterization and Biological Evaluation of Co(II), Cu(II), Ni(II) and Zn(II) Complexes With Cephradine

Some Co(II), Cu(II), Ni(II) and Zn(II) complexes of antibacterial drug cephradine have been prepared and characterized by their physical, spectral and analytical data. Cephradine acts as bidentate and the complexes have compositions, [M(L)2X2] where [M = Co(II), Ni(II) and Zn(II), L = cephradine and X = Cl2] showing octahedral geometry, and [M(L)2] where [M = Cu(II), L = cephradine] showing square planar geometry. In order to evaluate the effect of metal ions upon chelation, eephradine and its complexes have been screened for their antibacterial activity against bacterial strains, Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa

Risk Factors for Construction Workforce Safety towards Sustainability

This research article is based on the identification of safety risk factors associated with construction projects in Pakistan related with the China-Pakistan economic corridor (CPEC). In this paper, four construction sites have been targeted from Sindh, Punjab, Khyber Pakhtunkhwa, and Baluchistan province of Pakistan. The research was based on quantitative mode where the questionnaire survey was adopted for data collection and analysed statistically. The targeted respondents were 400 CPEC construction workforces from four different targeted sites in Pakistan. The collected data was analysed using descriptive statistical methods of Statistical Package of Social Sciences (SPSS) 23.0 software. According to the findings, it has been specified that the respondents from all four targeted construction sites in Pakistan has considered three major safety risk factors such as administrative, personal protective equipment (PPE) and workforce safety. Risk factors for administrative is between 1.06 and 2.65 (low level to moderate level), for PPE is between 1.06 and 2.65 (low level to moderate level) and for workforce safety is between 2.4 and 3.60 (moderate level to high Level). Meanwhile, the safety experts have been indicated the lack of proper training & PPE equipment’s, falling from height and falling object hazards are as the major cause of injuries at Pakistani construction sites related with CPEC projects. The findings of this study will be the catalyst for the CPEC projects in Pakistan to minimize the safety and health concern among construction industry workforce