94 research outputs found
Propagation losses in photonic crystal waveguides: Effects of band tail absorption and waveguide dispersion
Spectroscopy and Electrochemistry of Cobalt(III) Schiff Base Complexes
The structural, spectroscopic, and electrochemical properties of cobalt(III) derivatives of acacen (H_2acacen = bis(acetylacetone) ethylenediimine) and related ligands have been investigated. Electronic structure calculations indicate that the absorption between 340 and 378 nm in Co^(III)(acacen) spectra is attributable to the lowest π−π* intraligand charge-transfer transition. Equatorial ligand substitutions affect reduction potentials less than axial ligand changes, consistent with an electronic structural model in which d_(z^2) is populated in forming cobalt(II). The crystal structure of [Co(3-Cl-acacen)(NH_3)_2]BPh_4 has been determined: The compound crystallizes in the monoclinic space group (P2_1)/m (No. 11) with a = 9.720(2) Å, b = 18.142(4) Å, c = 10.046(2) Å, β = 100.11(3)°, D_c = 1.339 g cm^(-3), and Z = 2; the complex cation, [Co(3-Cl-acacen)(NH_3)_2]^+, exhibits a slightly distorted octahedral coordination geometry. The distances between the cobalt atom and the two axial nitrogen donor atoms differ only slightly (1.960(6) and 1.951(6) Å) and are similar to Co−N distances found in cobalt−ammine complexes as well as the axial Co−N distances in [Co(acacen)(4-MeIm)_2]Br·1.5H_2O; the latter compound crystallizes in the triclinic space group P1̄ (No. 2) with a = 18.466(9) Å, b = 14.936(7) Å, c = 10.111(5)Å, α = 96.27(5)°, β = 94.12(5)°, γ = 112.78(5)°, D_c = 1.447 g cm^(-3), and Z = 4
Free-Running 1550 nm VCSEL for 10.7 Gb/s Transmission in 99.7 km PON
We present a cooler-less, free-running 1550 nm vertical cavity surface emitting laser (VCSEL) directly modulated at 10.7 Gb/s. We also report on error-free transmission through 40 km of standard single-mode optical fiber, achieved without the use of dispersion-mitigation or mid-span amplification. Inverse-dispersion fiber was utilized to realize a dispersion-matched 99.7 km optical access uplink supporting error-free transmission with 27 dB loss margin. These results indicate the feasibility of implementing cooler-less long-wavelength VCSEL devices in long-reach optical access networks
Longitudinal‐mode control in integrated semiconductor laser phased arrays by phase velocity matching
MIMO-OFDM WDM PON with DM-VCSEL for femtocells application
Globalization, rapid technological changes, and growing competition not only facilitate but also make the supply chain more complex and fragile. Any disruption can disturb many organizations and even the whole system. There are many theories and frameworks that present a solution but no study is available that theoretically development framework for supply chain risk management. The focus of this study is to develop a novel framework for identifying the potential risks and assessment of their effects on supply chain performance. Additionally, evaluate the role of supply chain interaction in risk mitigation and performance improvement in Malaysian manufacturing. This is a conceptual paper, systematic as well as content analysis have been done for the literature review. For future study, there is a need to empirically verification of this theoretical framework. The proposed methodology to achieve this framework is; a questionnaire will be developed from a pool and will be validated by exploratory view for risk identification. This questionnaire will be distributed among Malaysian manufacturing and data will be analyzed through Structural Equation Modelling (SEM) for risk assessment and mitigation. The theoretical contribution of this study is support of the theory of swift, even flow as underpinning theory and information processing theory as supportive theory
EuCdAs: a magnetic semiconductor
EuCdAs is now widely accepted as a topological semimetal in which a
Weyl phase is induced by an external magnetic field. We challenge this view
through firm experimental evidence using a combination of electronic transport,
optical spectroscopy and excited-state photoemission spectroscopy. We show that
the EuCdAs is in fact a semiconductor with a gap of 0.77 eV. We show
that the externally applied magnetic field has a profound impact on the
electronic band structure of this system. This is manifested by a huge decrease
of the observed band gap, as large as 125~meV at 2~T, and consequently, by a
giant redshift of the interband absorption edge. However, the semiconductor
nature of the material remains preserved. EuCdAs is therefore a
magnetic semiconductor rather than a Dirac or Weyl semimetal, as suggested by
{\em ab initio} computations carried out within the local spin-density
approximation.Comment: Accepted for publication in Physical Review Letter
Spectroscopy and Electrochemistry of Cobalt(III) Schiff Base Complexes
The structural, spectroscopic, and electrochemical properties of cobalt(III) derivatives of acacen (H_2acacen = bis(acetylacetone) ethylenediimine) and related ligands have been investigated. Electronic structure calculations indicate that the absorption between 340 and 378 nm in Co^(III)(acacen) spectra is attributable to the lowest π−π* intraligand charge-transfer transition. Equatorial ligand substitutions affect reduction potentials less than axial ligand changes, consistent with an electronic structural model in which d_(z^2) is populated in forming cobalt(II). The crystal structure of [Co(3-Cl-acacen)(NH_3)_2]BPh_4 has been determined: The compound crystallizes in the monoclinic space group (P2_1)/m (No. 11) with a = 9.720(2) Å, b = 18.142(4) Å, c = 10.046(2) Å, β = 100.11(3)°, D_c = 1.339 g cm^(-3), and Z = 2; the complex cation, [Co(3-Cl-acacen)(NH_3)_2]^+, exhibits a slightly distorted octahedral coordination geometry. The distances between the cobalt atom and the two axial nitrogen donor atoms differ only slightly (1.960(6) and 1.951(6) Å) and are similar to Co−N distances found in cobalt−ammine complexes as well as the axial Co−N distances in [Co(acacen)(4-MeIm)_2]Br·1.5H_2O; the latter compound crystallizes in the triclinic space group P1̄ (No. 2) with a = 18.466(9) Å, b = 14.936(7) Å, c = 10.111(5)Å, α = 96.27(5)°, β = 94.12(5)°, γ = 112.78(5)°, D_c = 1.447 g cm^(-3), and Z = 4
Nucleocytoplasmic transport: a thermodynamic mechanism
The nuclear pore supports molecular communication between cytoplasm and
nucleus in eukaryotic cells. Selective transport of proteins is mediated by
soluble receptors, whose regulation by the small GTPase Ran leads to cargo
accumulation in, or depletion from the nucleus, i.e., nuclear import or nuclear
export. We consider the operation of this transport system by a combined
analytical and experimental approach. Provocative predictions of a simple model
were tested using cell-free nuclei reconstituted in Xenopus egg extract, a
system well suited to quantitative studies. We found that accumulation capacity
is limited, so that introduction of one import cargo leads to egress of
another. Clearly, the pore per se does not determine transport directionality.
Moreover, different cargo reach a similar ratio of nuclear to cytoplasmic
concentration in steady-state. The model shows that this ratio should in fact
be independent of the receptor-cargo affinity, though kinetics may be strongly
influenced. Numerical conservation of the system components highlights a
conflict between the observations and the popular concept of transport cycles.
We suggest that chemical partitioning provides a framework to understand the
capacity to generate concentration gradients by equilibration of the
receptor-cargo intermediary.Comment: in press at HFSP Journal, vol 3 16 text pages, 1 table, 4 figures,
plus Supplementary Material include
Vertical-external-cavity surface-emitting lasers and quantum dot lasers
The use of cavity to manipulate photon emission of quantum dots (QDs) has
been opening unprecedented opportunities for realizing quantum functional
nanophotonic devices and also quantum information devices. In particular, in
the field of semiconductor lasers, QDs were introduced as a superior
alternative to quantum wells to suppress the temperature dependence of the
threshold current in vertical-external-cavity surface-emitting lasers
(VECSELs). In this work, a review of properties and development of
semiconductor VECSEL devices and QD laser devices is given. Based on the
features of VECSEL devices, the main emphasis is put on the recent development
of technological approach on semiconductor QD VECSELs. Then, from the viewpoint
of both single QD nanolaser and cavity quantum electrodynamics (QED), a
single-QD-cavity system resulting from the strong coupling of QD cavity is
presented. A difference of this review from the other existing works on
semiconductor VECSEL devices is that we will cover both the fundamental aspects
and technological approaches of QD VECSEL devices. And lastly, the presented
review here has provided a deep insight into useful guideline for the
development of QD VECSEL technology and future quantum functional nanophotonic
devices and monolithic photonic integrated circuits (MPhICs).Comment: 21 pages, 4 figures. arXiv admin note: text overlap with
arXiv:0904.369
Multiple mobile excitons manifested as sidebands in metallic phase of TaSe<sub>3</sub>
Excitons are bound states between electrons and holes, whose charge neutrality and a priori itinerant nature make them interesting as potential transmitters of information. However, the demonstration of the mobility of such composite excitations has remained inaccessible to traditional optical experiments which only create and detect excitons with negligible momentum or group velocity. Here, we use angle-resolved photoemission spectroscopy (ARPES) to detect dispersing excitons in the quasi-one-dimensional metallic trichalcogenide TaSe3. While screening usually suppresses exciton formation in metals, the low density of conduction electrons, the low dimensionality, and two many-body effects in TaSe3 favor them. First, the conduction band is renormalized close to the Fermi surface, forming a band of heavy polarons. Second, the poorly screened interaction between a photo-induced valence hole and these polarons leads to various distinct excitonic bound states, which we interpret as intrachain and interchain excitons, and possibly even trions. The thresholds for the formation of a photohole together with an exciton show up in the form of unusual side bands in the ARPES spectra. They are nearly parallel to the bare valence band, but lie at lower excitation energies. Furthermore, we find that the energy separation of the side bands can be tuned by surface doping
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