Submillimeter-Wave Measurements and Analysis of the Ground and ν2 = 1 States of Water

In order to facilitate further studies of water in the interstellar medium, the envelopes of late-type stars, jets, and shocked regions, the frequencies of 17 newly measured H_2 ^(16)O transitions between 0.841 and 1.575 THz are reported. A complete update of the available water line frequencies and a detailed calculation of unmeasured rotational transitions and transition intensities as a function of temperature are presented for the ground and ν_2 = 1 state levels below 3000 cm^(-1) of excitation energy. The new terahertz transitions were measured with a recently developed laser difference frequency spectrometer. Six of these transitions arise from the ν_2 = 1 state, and the other 11 are in the ground state; all have lower state energies from 700 to 1750 cm^(-1) and should be accessible to Stratospheric Observatory For Infrared Astronomy (SOFIA) through the atmosphere. The transitions near 0.850 THz are accessible from the ground with existing receivers. Observations of the newly measured ν_2 = 1 state transitions, which include the 1_(1, 1)-0_(0, 0) fundamental at 1.2057 THz and five other very low J transitions, should provide valuable insights into role played by the ν2 = 1 state in the cooling dynamics of jets, shocks, masers, and strongly infrared-pumped regions. The line list is presented to assist in the planning of observational campaigns with the Far-Infrared Space Telescope (FIRST) and other proposed space missions with which a full suite of water observations can be carried out

A tunable cavity-locked diode laser source for terahertz photomixing

An all solid-state approach to the precise frequency synthesis and control of widely tunable terahertz radiation by differencing continuous-wave diode lasers at 850 nm is reported in this paper. The difference frequency is synthesized by three fiber-coupled external-cavity laser diodes. Two of the lasers are Pound-Drever-Hall locked to different orders of a Fabry-Perot (FP) cavity, and the third is offset-frequency locked to the second of the cavity-locked lasers using a tunable microwave oscillator. The first cavity-locked laser and the offset-locked laser produce the difference frequency, whose value is accurately determined by the sum of an integer multiple of the free spectral range of the FP cavity and the offset frequency. The dual-frequency 850-nm output of the three laser system is amplified to 500 mW through two-frequency injection seeding of a single semiconductor tapered optical amplifier. As proof of precision frequency synthesis and control of tunability, the difference frequency is converted into a terahertz wave by optical-heterodyne photomixing in low-temperature-grown GaAs and used for the spectroscopy of simple molecules. The 3-dB spectral power bandwidth of the terahertz radiation is routinely observed to be ≾1 MHz. A simple, but highly accurate, method of obtaining an absolute frequency calibration is proposed and an absolute calibration of 10^(-7) demonstrated using the known frequencies of carbon monoxide lines between 0.23-1.27 THz

A High Power Frequency-Stabilized Tunable Two-Frequency Diode Laser System for the Generation of Coherent THz-Waves by Photomixing

A tunable two-frequency high-power diode laser system at 850 nm for terahertz (Thz)-wave generation by photomixing in low-temperature-grown GaAs photo-conductors has been developed. The difference frequency is obtained through a three laser system, where two lasers are locked to different orders of a Fabry-Perot cavity and a third is offset-locked to the first, The difference-frequency signal is generated by the offset laser and the other cavity-locked laser. The spectral purity of the beat note is better than 1 MHz. The maximum output power of -500 mW was obtained by using the master oscillator power amplifier (MOPA) technique, simultaneous injection of two seed frequencies with a single semiconductor optical amplifier. Here we report the generation of THz waves and spectroscopy of acetonitrile as proof of concept

Entwicklungen von Drogenproblemen und Drogenpolitik in Großbritannien

'In Großbritannien sind die durch den Konsum illegaler Drogen verursachten Probleme erst spät zu einem öffentlichen Thema geworden. Der medizinische Konsum von Opium war im 19. Jahrhundert bekannt und mit dem Ersten Weltkrieg gab es eine kurze Episode des Kokainkonsums. Seit den 1920er Jahren führte das System des Rolleston-Komitees zu einem bemerkenswert niedrigen Niveau der Drogenabhängigkeit, aber das so genannte Britische System fand seinen Niedergang Ende der 1960er Jahre. Billiges Heroin aus dem Iran und Afghanistan wurde verfügbar, und das Rauchen von Heroin verbreitete sich insbesondere unter arbeitslosen Jugendlichen in Nordengland (Thatcher Ära). In den 1980er Jahren entwickelte sich die Strategie der Risikominimierung mit dem Ziel der Bekämpfung der Ausbreitung von HIV/ AIDS (Nadelaustausch). Gleichzeitig verschob sich die politische Agenda stärker in Richtung auf Kriminalitätskontrolle, wobei davon ausgegangen wurde, dass ein Drittel der kriminellen Delikte mit dem Konsum illegaler Drogen verbunden sei. Allerdings bleibt Cannabis die am meisten konsumierte Droge mit etwa 3-5 Millionen regelmäßigen Konsumenten und Konsumentinnen, wobei sich diese Zahl zu reduzieren scheint, auch wenn man hierfür bislang keine Gründe angeben kann.' (Autorenreferat)'Britain was something of a late developer in terms of problems with illicit drugs. The use of opium and morphine in various medicinal products was not unknown in the 19th century, and during the 1914-18 War there was a brief episode of cocaine use. However, after the adoption of the Rolleston committee system in the 1920s, the level of drug addiction remained remarkably low but the so-called 'British system' broke down in the late 1960s. Heroin in cheap and plentiful supply became suddenly available from Iran and Afghanistan. The habit of 'chasing the dragon' spread like a whirlwind among the young unemployed (this was the Thatcher's period) in many towns and cities in the north of England. A dominant policy response to this epidemic from the late 1980s onwards was the promotion of 'harm reduction' strategies to combat the spread of HIV/AIDS (such as needle exchange schemes). The policy agenda has also shifted, away towards a crime-control approach with one-third or more of crime being estimated to be drug-related, especially to heroin and Crack-cocaine. The most commonly used drug in Britain remains cannabis, with probably 3-5 million regular users, and quite recently the penalties for cannabis possession have been reduced; and since then the level of cannabis use has fallen a little. But why is unknown.' (author's abstract

Proprioceptive perception of phase variability

Previous work has established that judgments of relative phase variability of 2 visually presented oscillators covary with mean relative phase. Ninety degrees is judged to be more variable than 0° or 180°, independently of the actual level of phase variability. Judged levels of variability also increase at 180°. This pattern of judgments matches the pattern of movement coordination results. Here, participants judged the phase variability of their own finger movements, which they generated by actively tracking a manipulandum moving at 0°, 90°, or 180°, and with 1 of 4 levels of Phase Variability. Judgments covaried as an inverted U-shaped function of mean relative phase. With an increase in frequency, 180° was judged more variable whereas 0° was not. Higher frequency also reduced discrimination of the levels of Phase Variability. This matching of the proprioceptive and visual results, and of both to movement results, supports the hypothesized role of online perception in the coupling of limb movements. Differences in the 2 cases are discussed as due primarily to the different sensitivities of the systems to the information

Traveling-Wave Photomixers Based On Noncollinear Optical/Terahertz Phase-Matching

Traveling-wave THz photomixers based on angle-tuned optical/THz phase-matching are experimentally demonstrated. A dc-biased coplanar stripline terminated by a planar antenna is fabricated on low-temperature-grown GaAs. A distributed area between the striplines is illuminated by two noncollinear laser beams which generate interference fringes accompanied by THz waves. The velocity of the optical fringe is matched to the THz-wave velocity in the stripline by tuning the incident angle of the laser beams. The device can handle the laser power over 300 mW and provides the THz output of ~0.1 µW with the 3-dB bandwidth of 2 THz. The experimental results show that traveling-wave photomixers have the potential to surpass conventional small area designs

Design and characterization of optical-THz phase-matched traveling-wave photomixers

Design and characterization of optical-THz phase-matched traveling-wave photomixers for difference-frequency generation of THz waves are presented. A de-biased coplanar stripline fabricated on low-temperature-grown GaAs is illuminated by two non-collinear laser beams which generate moving interference fringes that are accompanied by THz waves. By tuning the offset angle between the two laser beams, the velocity of the interference fringe can be matched to the phase velocity of the THz wave in the coplanar stripline. The generated THz waves are radiated into free space by the antenna at the termination of the stripline. Enhancement of the output power was clearly observed when the phase-matching condition was satisfied. The output power spectrum has a 3-dB bandwidth of 2 THz and rolls off as ~9 dB/Oct which is determined by the frequency dependent attenuation in the stripline, while the bandwidth of conventional photomixer design has the limitation by the RC time constant due to the electrode capacitance. The device can handle the laser power of over 380 mW, which is 5 times higher than the maximum power handring capability of conventional small area devices. The results show that the traveling-wave photomixers have the potential to surpass small area designs, especially at higher frequencies over I THz, owing to their great thermal dissipation capability and capacitance-free wide bandwidth

A traveling-wave THz photomixer based on angle-tuned phase matching

A traveling-wave THz photomixer based on a free-space optical-THz phase-matching scheme is proposed. A dc-biased coplanar strip line fabricated on low-temperature-grown GaAs serves as the active area of the device, and is illuminated by two noncollinear laser beams which generate interference fringes that are accompanied by THz waves. The device with the laser-power-handling capability over 300 mW and a 3-dB bandwidth of 1.8 THz was experimentally demonstrated. The results show that traveling-wave photomixers have the potential to surpass small-area designs

Socio-technical transitions in UK electricity: part 1 – history, actors and pathways

A large interdisciplinary consortium of engineers, social scientists and policy analysts has developed three low-emissions, more-electric transition pathways for the UK. The approach is based on earlier work on understanding transitions, applying a multi-level perspective with landscape, regime and niche levels to the development of sociotechnical scenarios. The pathways to 2050 focus on the power sector, including the potential for increasing the use of low-emissions electricity for heating and transport. Part 1 describes studies of historical energy and infrastructure transitions that help to understand the dynamics and timing of past transitions. The role of large-scale and small-scale actors in the electricity sector and methods used to develop the pathways are then described. In part 2, associated technologies are evaluated to determine the choices that need to be made by UK energy policymakers and stakeholders. All three pathways are appraised in terms of their environmental performance using complementary life-cycle assessment and footprinting methods. Lessons can clearly be drawn for other industrialised nations attempting to reduce the emissions from their electricity generation systems, although local circumstances will determine country- and region-specific options