2,808 research outputs found
Microcystin-leucine arginine causes cytotoxic effects in sertoli cells resulting in reproductive dysfunction in male mice
2016-2017 > Academic research: refereed > Publication in refereed journal201804_a bcmaVersion of RecordPublishe
Silver-based surface plasmon waveguide for terahertz quantum cascade lasers
Terahertz quantum cascade lasers (THz QCLs) have undergone rapid developments since their first demonstration in 2002. Presently, the wide spectral range (1.2–5.2 THz) and high output power (1 W) make THz QCLs promising sources for applications in high-resolution spectroscopy and THz imaging. However, their maximum operating temperature is only 199.5 K and therefore cryogenic cooling is still needed. Improving the thermal performance of THz QCLs is a key challenge for their practical usage. The waveguide loss is closely related with the device thermal performance. To lower the loss, copper has been used to replace the gold in the standard metal–metal waveguide scheme, and around 10 K increase in the maximum lasing temperature has been achieved. Here, we employ silver as the waveguide metal and investigate its effects on devices with a single surface-plasmon waveguide configuration
Canonical quantization of non-commutative holonomies in 2+1 loop quantum gravity
In this work we investigate the canonical quantization of 2+1 gravity with
cosmological constant in the canonical framework of loop quantum
gravity. The unconstrained phase space of gravity in 2+1 dimensions is
coordinatized by an SU(2) connection and the canonically conjugate triad
field . A natural regularization of the constraints of 2+1 gravity can be
defined in terms of the holonomies of . As a first step
towards the quantization of these constraints we study the canonical
quantization of the holonomy of the connection on the
kinematical Hilbert space of loop quantum gravity. The holonomy operator
associated to a given path acts non trivially on spin network links that are
transversal to the path (a crossing). We provide an explicit construction of
the quantum holonomy operator. In particular, we exhibit a close relationship
between the action of the quantum holonomy at a crossing and Kauffman's
q-deformed crossing identity. The crucial difference is that (being an operator
acting on the kinematical Hilbert space of LQG) the result is completely
described in terms of standard SU(2) spin network states (in contrast to
q-deformed spin networks in Kauffman's identity). We discuss the possible
implications of our result.Comment: 19 pages, references added. Published versio
Modelling of three-well extraction-controlled terahertz frequency quantum cascade lasers using an extended density matrix approach
Terahertz frequency quantum cascade lasers for use as waveguide-integrated local oscillators
Since their first demonstration in 2002, the performance of terahertz frequency quantum cascade lasers has developed extremely rapidly. We consider the potential use of terahertz frequency quantum cascade lasers as local oscillators in satellite-borne instrumentation for future Earth observation and planetary science missions. A specific focus will be on the development of compact, waveguide-integrated, heterodyne detection systems for the supra-terahertz range
Feedhorn-integrated THz QCL local oscillators for the LOCUS atmospheric sounder
The LOCUS atmospheric sounder is a satellite-borne THz radiometer concept, for studying molecular species in the mesosphere and lower thermosphere. We report waveguide-integrated THz quantum-cascade lasers for use as 3.5 THz local oscillators. A waveguide-integration scheme, using an integrated diagonal feedhorn significantly improves power outcoupling. 1.3 mW THz emission is demonstrated in a space-qualified Stirling cryocooler at 57 K, with ∼15° beam divergence
Extraction-controlled terahertz frequency quantum cascade lasers with a diagonal LO-phonon extraction and injection stage
We report an extraction-controlled terahertz (THz)-frequency quantum cascade laser design in which a diagonal LO-phonon scattering process is used to achieve efficient current injection into the upper laser level of each period and simultaneously extract electrons from the adjacent period. The effects of the diagonality of the radiative transition are investigated, and a design with a scaled oscillator strength of 0.45 is shown experimentally to provide the highest temperature performance. A 3.3 THz device processed into a double-metal waveguide configuration operated up to 123 K in pulsed mode, with a threshold current density of 1.3 kA/cm2 at 10 K. The QCL structures are modeled using an extended density matrix approach, and the large threshold current is attributed to parasitic current paths associated with the upper laser levels. The simplicity of this design makes it an ideal platform to investigate the scattering injection process
Functional cartography of complex metabolic networks
High-throughput techniques are leading to an explosive growth in the size of
biological databases and creating the opportunity to revolutionize our
understanding of life and disease. Interpretation of these data remains,
however, a major scientific challenge. Here, we propose a methodology that
enables us to extract and display information contained in complex networks.
Specifically, we demonstrate that one can (i) find functional modules in
complex networks, and (ii) classify nodes into universal roles according to
their pattern of intra- and inter-module connections. The method thus yields a
``cartographic representation'' of complex networks. Metabolic networks are
among the most challenging biological networks and, arguably, the ones with
more potential for immediate applicability. We use our method to analyze the
metabolic networks of twelve organisms from three different super-kingdoms. We
find that, typically, 80% of the nodes are only connected to other nodes within
their respective modules, and that nodes with different roles are affected by
different evolutionary constraints and pressures. Remarkably, we find that
low-degree metabolites that connect different modules are more conserved than
hubs whose links are mostly within a single module.Comment: 17 pages, 4 figures. Go to http://amaral.northwestern.edu for the PDF
file of the reprin
Waveguide-integrated Terahertz Quantum Cascade Lasers for use as Local Oscillators
Terahertz-frequency quantum cascade lasers (THz QCLs) are compact sources of 1–5 THz radiation, which show great promise for use as local oscillators in satellite-borne heterodyne radiometers. We present a waveguide-integration scheme, in which a THz QCL is mounted in a copper heat-sink block, with radiation outcoupled into a precision micromachined rectangular waveguide. Electrical bias is provided by an integrated SMA connector and mounting points are provided for attachment to a cryocooler and a temperature sensor. The integration scheme is mechanically robust and is shown to have negligible impact on the thermal performance or threshold current of the device. The emitted beam quality is significantly improved, compared with that of a conventional device, with single-lobed profile with divergence <20 degrees
Waveguide-integrated terahertz-frequency quantum cascade lasers for detection of trace-gas species
We demonstrate high-performance THz QCLs lasing at 2.2, 2.53, 3.5 and 4.7 THz, which target absorption lines of water, methane, hydroxyl and atomic oxygen respectively. Reliable single-mode targeting of gas species is obtained through the use of a photonic lattice design. A highly reproducible micro-machined waveguide block yields narrow beam-divergence and enables future integration of a complete THz heterodyne system including local-oscillator, mixer, and feed-horn
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