Correction to "Mode Selection and Tuning Mechanisms in Coupled-Cavity Terahertz Quantum Cascade Lasers"

In [1], the affiliation for Andrew Grier was incorrect. The correct affiliation where his contribution was made is as follows: A. T. Grier was with the School of Electronic and Electrical Engineering, University of Leeds, LS2 9JT Leeds, U.K. (e-mail: [email protected])

Mode selection and tuning mechanisms in coupled-cavity terahertz quantum cascade lasers

We present a model for longitudinal mode competition in coupled-cavity (CC) terahertz (THz) quantum cascade lasers (QCLs) by using a scattering matrix method and multi-mode reduced rate equations (RREs). The dependence of the mode selection and tuning characteristics on various device parameters are systematically investigated, including the net waveguide loss, the optical length of the passive cavity, and the heat sink temperature for different relationship between the active and passive cavity lengths. The changes in eigenmode frequencies due to variations of device parameter are calculated before solving the RREs. The mode selection and tuning results obtained from solving the nonlinear RREs could be well explained by linear scattering matrix analysis. The mode tuning process simulated by the proposed model is compared with experimentally measured data, yielding good agreement. Comprehensive study of the influence of the key device parameters on the performance of CC THz QCLs provides potential design rules for single-mode operation with either wide frequency tunability or high stability

Impacts of local human activities on the Antarctic environment

We review the scientific literature, especially from the past decade, on the impacts of human activities on the Antarctic environment. A range of impacts has been identified at a variety of spatial and temporal scales. Chemical contamination and sewage disposal on the continent have been found to be long-lived. Contemporary sewage management practices at many coastal stations are insufficient to prevent local contamination but no introduction of non-indigenous organisms through this route has yet been demonstrated. Human activities, particularly construction and transport, have led to disturbances of flora and fauna. A small number of non-indigenous plant and animal species has become established, mostly on the northern Antarctic Peninsula and southern archipelagos of the Scotia Arc. There is little indication of recovery of overexploited fish stocks, and ramifications of fishing activity oil bycatch species and the ecosystem could also be far-reaching. The Antarctic Treaty System and its instruments, in particular the Convention for the Conservation of Antarctic Marine Living Resources and the Environmental Protocol, provide a framework within which management of human activities take place. In the face of the continuing expansion of human activities in Antarctica, a more effective implementation of a wide range of measures is essential, in order to ensure comprehensive protection of the Antarctic environment, including its intrinsic, wilderness and scientific values which remains a fundamental principle of the Antarctic Treaty System. These measures include effective environmental impact assessments, long-term monitoring, mitigation measures for non-indigenous species, ecosystem-based management of living resources, and increased regulation of National Antarctic Programmes and tourism activities

Cellular and humoral immune responses and protection against schistosomes induced by a radiation-attenuated vaccine in chimpanzees

The radiation-attenuated Schistosoma mansoni vaccine is highly effective in rodents and primates but has never been tested in humans, primarily for safety reasons. To strengthen its status as a paradigm for a human recombinant antigen vaccine, we have undertaken a small-scale vaccination and challenge experiment in chimpanzees (Pan troglodytes). Immunological, clinical, and parasitological parameters were measured in three animals after multiple vaccinations, together with three controls, during the acute and chronic stages of challenge infection up to chemotherapeutic cure. Vaccination induced a strong in vitro proliferative response and early gamma interferon production, but type 2 cytokines were dominant by the time of challenge. The controls showed little response to challenge infection before the acute stage of the disease, initiated by egg deposition. In contrast, the responses of vaccinated animals were muted throughout the challenge period. Vaccination also induced parasite-specific immunoglobulin M (IgM) and IgG, which reached high levels at the time of challenge, while in control animals levels did not rise markedly before egg deposition. The protective effects of vaccination were manifested as an amelioration of acute disease and overall morbidity, revealed by differences in gamma-glutamyl transferase level, leukocytosis, eosinophilia, and hematocrit. Moreover, vaccinated chimpanzees had a 46% lower level of circulating cathodic antigen and a 38% reduction in fecal egg output, compared to controls, during the chronic phase of infection

Pathological and ecological host consequences of infection by an introduced fish parasite

The infection consequences of the introduced cestode fish parasite Bothriocephalus acheilognathi were studied in a cohort of wild, young-of-the-year common carp Cyprinus carpio that lacked co-evolution with the parasite. Within the cohort, parasite prevalence was 42% and parasite burdens were up to 12% body weight. Pathological changes within the intestinal tract of parasitized carp included distension of the gut wall, epithelial compression and degeneration, pressure necrosis and varied inflammatory changes. These were most pronounced in regions containing the largest proportion of mature proglottids. Although the body lengths of parasitized and non-parasitized fish were not significantly different, parasitized fish were of lower body condition and reduced weight compared to non-parasitized conspecifics. Stable isotope analysis (δ15N and δ13C) revealed trophic impacts associated with infection, particularly for δ15N where values for parasitized fish were significantly reduced as their parasite burden increased. In a controlled aquarium environment where the fish were fed ad libitum on an identical food source, there was no significant difference in values of δ15N and δ13C between parasitized and non-parasitized fish. The growth consequences remained, however, with parasitized fish growing significantly slower than non-parasitized fish, with their feeding rate (items s−1) also significantly lower. Thus, infection by an introduced parasite had multiple pathological, ecological and trophic impacts on a host with no experience of the parasite

Future Seismic Hazards in Southern California - Phase I: Implications of the 1992 Landers Earthquake Sequence

Southern California and its seismologists received a wake-up call on June 28, 1992. The largest earthquake to strike southern California in 40 years occurred near the town of Landers, located 30 km north of the San Andreas fault. It had a magnitude of 7.5 (M7.5). Three and one-half hours later, a M6.5 aftershock struck the Big Bear area 40 km (kilometers) to the west of Landers. An ad hoc working group was rapidly convened in July, 1992, to evaluate how the Landers-Big Bear earthquake sequence might affect future large earthquakes along major faults in southern California. In particular, what are the chances of large earthquakes in the next few years and how do they compare to previous estimates (such as those of the Working Group on California Earthquake Probabilities -- WGCEP, 1988)? Such an evaluation was made for central California after the Lorna Prieta earthquake of 1989 (WGCEP, 1990). The charge to the Landers ad hoc working group included analyzing the seismicity for the last several years in southern California and the new paleoseismic, geologic, and geodetic data recently available for southern California. To inform the public about the potential hazard of plausible earthquakes, the working group was also asked to map the predicted severity of ground shaking for such earthquakes compared to that from the Landers earthquake

Origin of terminal voltage variations due to self-mixing in a terahertz frequency quantum cascade laser

The use of quantum cascade lasers (QCLs) for laser feedback interferometry (LFI) has received significant attention since it enables a wide range of sensing applications without requiring a separate detector, and hence simplifies experimental apparatus [1]. LFA (based on the self-mixing effect) refers to the partial reinjection of the radiation emitted from a laser after reflection from a target; the injected radiation field then interacts with the intra-cavity field causing measurable variations of the QCL terminal voltage. The theory of LFI with conventional laser sources is well studied and explained by the Lang–Kobayashi model [2, 3]. However, while this enables the dynamic state populations and light interaction to be modelled, a linear relationship between the change in cavity light power, ∆P, and terminal voltage variation is commonly assumed, i.e. VSM ∝ ∆P [4, 5]. This is not strictly applicable to QCL structures since carrier transport is dominated by the mechanisms of electron subband alignment, intersubband scattering and photon driven transport between subbands with energy separations that change with applied bias (terminal voltage). We present experimental results of a QCL which departs significantly from this assumed linear behavior. We observe strong enhancement of the self-mixing signal in regions where the local gradient of the current-voltage (I–V) curve increases. We explain the origin of this signal using an extended density matrix (DM) approach [6] which accounts for coherent transport and interaction of the optical light field with the active region. The model is used to calculate the I–V characteristics of a bound-to-continuum (BTC) terahertz (THz) QCL and predict the effect of light variation on terminal voltage at a fixed drive current. This approach is shown to predict the experimental signal with good agreement

Homothetic perfect fluid space-times

A brief summary of results on homotheties in General Relativity is given, including general information about space-times admitting an r-parameter group of homothetic transformations for r>2, as well as some specific results on perfect fluids. Attention is then focussed on inhomogeneous models, in particular on those with a homothetic group $H_4$ (acting multiply transitively) and $H_3$. A classification of all possible Lie algebra structures along with (local) coordinate expressions for the metric and homothetic vectors is then provided (irrespectively of the matter content), and some new perfect fluid solutions are given and briefly discussed.Comment: 27 pages, Latex file, Submitted to Class. Quantum Gra