A novel noncontacting waveguide backshort for millimeter and submillimeter wave frequencies

A new noncontacting waveguide backshort was developed for millimeter and submillimeter wave frequencies. It employs a metallic bar with rectangular or circular holes. The size and spacing of the holes are adjusted to provide a periodic variation of the guide impedance on the correct length scale to give a large reflection of RF frequency power. This design is mechanically rugged and can be easily fabricated for millimeter wave frequencies above 300 GHz where conventional backshorts are difficult to fabricate. Model experiments were performed at 4 to 6 GHz to optimize the design. Values of reflected power greater than 95 percent over a 30 percent bandwidth were achieved. The design was scaled to WR-10 band (75 to 110 GHz) with comparably good results

Geographies of the body and the histories of photography

Informed by feminist epistemologies, cultural theory and social history, the thesis takes as its primary focus discourses of gender and sexuality in the field of photographic culture. The accompanying contextualisation reflects the shifting theoretical and methodological terrain of visual cultural studies over the historical period in question (1983 - 2003). Earlier articles cover the project's initial development and subsequent essays navigate the work into a more historical context culminating in Seeing her Sex: Medical Archives and the Female Body (2002). This book draws forms the main body of the submission. It draws upon theories of feminism and sexual difference, the histories of mass-reproducible visual technologies and the philosophy of science in order to understand how human generation became female reproduction. Thus it places photography within a longer historical framework of visual technologies (engraving, lithography, stereoscopy, radiography and microscopy) that amalgamated to produce new kinds of objects and observers. It offers vertical 'deep' studies of particular historical images, and also more lateral, horizontal connections across disciplines. Its approach is therefore interdisciplinary and engages in an argument about the historical and geographical boundaries of knowledge, about what comes before and after and about what gets to lie inside and outside the discursive field of photography. This work examines and develops arguments that are always located in, but also move beyond, the archive. The essays included here re-think questions of visual representation and discursive formations in order to foreground the inter-connected relationships between institutional, cultural and embodied aspects of scholarship. Within the field of visual cultural studies the question of agency and the relationship between theories, histories and politics became urgent in the political climate of the 1980s and 1990s. Increasingly questions of the subject's participation, cultural location and perspective in constructing any 'field' or 'terrain' became important and the relationship between experience and theory has consequently been re-thought. In the later publications the body is therefore discussed as both subject and object of visual knowledge. The work argues against an essentialist understanding of what any 'body' is, and for an understanding of the body in its material and historical corporeality, rather than its biological specificity. Understood as subjective and embodied, situated and partial, this more phenomenological, intersubjective approach to visual cultural studies acknowledges the sensory, emotional and imaginative dimensions of looking. Knowledge here is conceptualised not as possession, but as empathy. What we see as observers depends not only on where we stand but also on how we position ourselves within any given historical field. Moreover, this is a political question; not all perspectives are equal. This work has grown out of an antipathy to the disembodied approach of the humanities within which the human body had become alienated, suspect, denigrated. In its drive for fixed standards, the human sciences subordinated body to mind, emotion to reason thus foreclosing crucial sensory aspects of knowledge and creating an incapacity to acknowledge the wide diversity of our different modes of knowing. Historically, photography certainly does have an ignoble history as a technology of ethnographic domination and control (imperial, colonial, racial or sexual), but it is also, equally, a form of counter-memory. Images are a question of human rights and here visual cultural studies has a key role to play

The impact of Arctic sea ice on the Arctic energy budget and on the climate of the Northern mid-latitudes

The atmospheric general circulation model EC-EARTH-IFS has been applied to investigate the influence of both a reduced and a removed Arctic sea ice cover on the Arctic energy budget and on the climate of the Northern mid-latitudes. Three 40-year simulations driven by original and modified ERA-40 sea surface temperatures and sea ice concentrations have been performed at T255L62 resolution, corresponding to 79 km horizontal resolution. Simulated changes between sensitivity and reference experiments are most pronounced over the Arctic itself where the reduced or removed sea ice leads to strongly increased upward heat and longwave radiation fluxes and precipitation in winter. In summer, the most pronounced change is the stronger absorption of shortwave radiation which is enhanced by optically thinner clouds. Averaged over the year and over the area north of 70° N, the negative energy imbalance at the top of the atmosphere decreases by about 10 W/m2 in both sensitivity experiments. The energy transport across 70° N is reduced. Changes are not restricted to the Arctic. Less extreme cold events and less precipitation are simulated in sub-Arctic and Northern mid-latitude regions in winter

Photon induced secondary electron emission

Numerical models for predicting photon-induced secondary electron emission are presented. The results are compared with experimental measurements made using a Co-60 gamma ray source

A 100 GHz coplanar strip circuit tuned with a sliding planar backshort

A means of mechanically altering the electrical length of a planar transmission line would greatly enhance the use of integrated circuit technology at millimeter and submillimeter wavelengths. Such a mechanically adjustable planar RF tuning element, successfully demonstrated at 100 GHz, is described here. It consists of a thin metallic sheet, with appropriately sized and spaced holes, which slides along on top of a dielectric-coated coplanar-strip transmission line. Multiple RF reflections caused by this structure add constructively, resulting in a movable RF short circuit, with |s11|≫APX=/-0.3 dB, which can be used to vary the electrical length of a planar tuning stub. The sliding short is used here to produce a 2-dB improvement in the response of a diode detector. This tuning element can be integrated with planar circuits to compensate for the effect of parasitic reactance inherent in various devices including semiconductor diodes and superconductor-insulator-superconductor (SIS) junctions

Silicon micromachined waveguides for millimeter-wave and submillimeter-wave frequencies

The development of micromachining techniques to create silicon-based waveguide circuits, which can operate up to high submillimeter-wave frequencies, is reported. As a first step, a WR-10 waveguide has been fabricated from (110) silicon wafers. Insertion loss measurements on a gold-plated silicon waveguide show performance comparable to that of standard metal waveguides. It is suggested that active devices and planar circuits can be integrated with the waveguides, solving the traditional mounting problems

Pre-hospital management of acute Addison’s Disease – Audit of patients attending a referral hospital in a regional area

Context: Adrenal crises (AC) cause morbidity and mortality in patients with Addison’s disease [primary adrenal insufficiency (PAI)]. Patient-initiated oral stress dosing, with parenteral hydrocortisone, is recommended to avert ACs. While these should be effective, the continued incidence of ACs remains largely unexplained. Methods: Audit of all attendances between 2000 and 2017 by adult patients with treated PAI to one large regional referral centre in New South Wales, Australia. Measurements were those taken on arrival at hospital. Results: There were 252 attendances by 56 patients with treated PAI during the study period. Women comprised 60.7% (n=34) of the patients. The mean age of attendees was 53.7 (19.6) years. Nearly half (45.2%, n=114) the patients had an infection. There were 61 (24.2%) ACs diagnosed by the treating clinician. Only 17.9% (n=45) of the hospital presentations followed any form of stress dosing. IM hydrocortisone was used before 7 (2.8%) attendances only. Among patients with a clinician diagnosed AC, only 32.8% (n=20) had used stress dosing before presentation. Vomiting was reported by 47.6% (n=120) of the patients but only 33 (27.5%) of these attempted stress dosing and 5 patients with vomiting used IM hydrocortisone. The number of prior presentations was a significant independent predictor of use of stress doses [1.05 (1.01,1.09)]. Conclusion: Dose escalation strategies are not used universally or correctly by unwell patients with PAI, many patients do not use IM or SC hydrocortisone injections. Previous hospital treatment increases the likelihood of stress dosing and offers the opportunity for reinforcement of prevention strategies

Noncontacting waveguide backshort

A noncontacting waveguide backshort is provided for use with frequencies of interest between 1 and 1000 GHz including a relatively rugged metallic bar movably mounted within the waveguide in a MYLAR insulator. A series of regularly shaped and spaced circular or rectangular openings are made in the metallic bar to form sections of high impedance alternating with sections of the bar having low impedance. This creates a periodic impedance variation which serves to provided an adjustable short circuit in a waveguide for the frequencies of interest

An adjustable RF tuning element for microwave, millimeter wave, and submillimeter wave integrated circuits

Planar RF circuits are used in a wide range of applications from 1 GHz to 300 GHz, including radar, communications, commercial RF test instruments, and remote sensing radiometers. These circuits, however, provide only fixed tuning elements. This lack of adjustability puts severe demands on circuit design procedures and materials parameters. We have developed a novel tuning element which can be incorporated into the design of a planar circuit in order to allow active, post-fabrication tuning by varying the electrical length of a coplanar strip transmission line. It consists of a series of thin plates which can slide in unison along the transmission line, and the size and spacing of the plates are designed to provide a large reflection of RF power over a useful frequency bandwidth. Tests of this structure at 1 GHz to 3 Ghz showed that it produced a reflection coefficient greater than 0.90 over a 20 percent bandwidth. A 2 GHz circuit incorporating this tuning element was also tested to demonstrate practical tuning ranges. This structure can be fabricated for frequencies as high as 1000 GHz using existing micromachining techniques. Many commercial applications can benefit from this micromechanical RF tuning element, as it will aid in extending microwave integrated circuit technology into the high millimeter wave and submillimeter wave bands by easing constraints on circuit technology