Optical gyroscope system

Light beams pass in opposite directions through a single mode fiber optic wave guide that extends in a circle or coil in an optical gyroscope system which measures the rotation rate of the coil by measuring the relative phase shifts of the beams by interferometric techniques. Beam splitting and phase shifting of the light are facilitated by utilizing brief pulses of light and by using light-controlling devices which are operated for a brief time only when the light pulse passes in one direction through the device but not at a different time when the pulse is passing in the opposite direction through the device. High accuracy in rotation measurement is achieved at both very slow and very fast rotation rates, by alternately operating the system so that at zero rotation the interfering waves are alternately 90 out of phase and in phase. Linear polarization of the light beams is maintained by coiling the full length of the optic fiber in a single plane

Wilbur Norman Christiansen 1913-2007

W. N. ('Chris') Christiansen was an innovative and influential radio astronomy pioneer. The hallmarks of his long and distinguished career in science and engineering, spanning almost five decades, were his inventiveness and his commitment to, and success with, large-scale projects. These projects were the outcome of his innovative skill as physicist and engineer. Paralleling this was his equal commitment to forging strong international links and friendships, leading to his election as Vice-President of the International Astronomical Union for the years 1964 to 1970, as President of the International Union of Radio Science, URSI, from 1978 to 1981, and subsequently as Honorary Life President in 1984, and as Foreign Secretary of the Australian Academy of Science from 1981 to 1985. Major subsequent developments in radio astronomy and wireless communications on the global scene stand as a legacy to Chris's approach to his work and to the development of those who worked with him.Comment: 16 pages, 4 figure

Continuing education: The 1998 survey of the Royal Australasian College of Dental Surgeons

The document attached has been archived with permission from the Australian Dental Association. An external link to the publisher’s copy is included.Background: Continuing education (CE) is an essential professional activity. In the last decade, CE has been actively pursued by the medical profession in Australia and abroad. However, the uptake of CE in dentistry has been much slower and there is minimal Australian data on dental CE. Methods: To determine the level of CE activity, in 1998, postal questionnaires were sent to all fellows of the Royal Australasian College of Dental Surgeons. The responses were analysed. Results: There was a high reponse rate (90 per cent) but a moderate usable rate (54 per cent). The results show a biphasic distribution between high and low CE activity. The average amount of activity of those involved in CE was 116 hours per year, above the usually accepted minimum of 100 hours/year. Some groups, particularly members of the specialist divisions of oral and maxillofacial surgeons (215 hours) and periodontists (205 hours), have high levels of CE. However, approximately 25 per cent of college fellows reported little or no CE activity. The survey revealed that inactive fellows are more likely to be older and in general practice. Inactive fellows were also tardy in replying to the questionnaire. Conclusion: The high activity CE group needs to be recognised and encouraged to continue. Specific plans to help the low CE activity group should be developed. Although these findings relate directly to the Royal Australasian College of Dental Surgeons, they are presented as they have implications for the dental profession at large.P Sambrook, D Thomson, R Bastiaan and A Gos

A New Perspective of the Radio Bright Zone at The Galactic Center: Feedback from Nuclear Activities

New observations of Sgr A have been carried out with the VLA using the broadband (2 GHz) continuum mode at 5.5 GHz, covering the central 30 pc region of the RBZ at the Galactic center. Using the MS-MFS algorithms in CASA, we have imaged Sgr A with a resolution of 1", achieving an rms 8 $\mu$Jy/beam, and a dynamic range 100,000:1.The radio image is compared with X-ray, CN emission-line and Paschen-$\alpha$ images obtained using Chandra, SMA and HST/NICMOS, respectively. We discuss several prominent radio features. The "Sgr A West Wings" extend 5 pc from the NW and SE tips of the ionized "Mini-spiral" in Sgr A West to positions located 2.9 and 2.4 arc min to the NW and SE of Sgr A*, respectively. The NW wing, along with several other prominent features, including the "NW Streamers", form an elongated radio lobe (NW lobe), oriented nearly perpendicular to the Galactic plane. This radio lobe, with a size of 14.4 pc x 7.3 pc, has a known X-ray counterpart. A row of three thermally emitting rings is observed in the NW lobe. A field containing numerous amorphous radio blobs extends for a distance of ~2 arc min beyond the tip of the SE wing; these features coincide with the SE X-ray lobe. Most of the amorphous radio blobs in the NW and SE lobes have Paschen-$\alpha$ counterparts, suggesting that a shock interaction of ambient gas concentrations with a collimated nuclear wind (outflow) that may be driven by radiation force from the central star cluster within the CND. Finally, we remark on a prominent radio feature located within the shell of the Sgr A East SNR. Because this feature -- the "Sigma Front" -- correlates well in shape and orientation with the nearby edge of the CND, we propose that it is a reflected shock wave resulting from the impact of the Sgr A East blast wave on the CND.Comment: 18 pages, 9 figures, ApJ accepte

WSRT and VLA Observations of the 6 cm and 2 cm lines of H2CO in the direction of W 58 C1(ON3) and W 58 C2

Absorption in the J{K-K+} = 2{11}-2{12} transition of formaldehyde at 2 cm towards the ultracompact HII regions C1 and C2 of W 58 has been observed with the VLA with an angular resolution of ~0.2'' and a velocity resolution of ~1 km/s. The high resolution continuum image of C1 (ON 3) shows a partial shell which opens to the NE. Strong H2CO absorption is observed against W 58 C1. The highest optical depth (tau > 2) occurs in the SW portion of C1 near the edge of the shell, close to the continuum peak. The absorption is weaker towards the nearby, more diffuse compact HII region C2, tau<~0.3. The H2CO velocity (-21.2 km/s) towards C1 is constant and agrees with the velocity of CO emission, mainline OH masers, and the H76 alpha recombination line, but differs from the velocity of the 1720 MHz OH maser emission (~-13 km/s). Observations of the absorption in the J{K-K+} = 1{10}-1{11} transition of formaldehyde at 6 cm towards W 58 C1 and C2 carried out earlier with the WSRT at lower resolution (~4''x7'') show comparable optical depths and velocities to those observed at 2 cm. Based on the mean optical depth profiles at 6 cm and 2 cm, the volume density of molecular hydrogen n(H2) and the formaldehyde column density N(H2CO) were determined. The n(H2) is ~6E4 /cm**3 towards C1. N(H2CO) for C1 is ~8E14 /cm**2 while that towards C2 is ~8E13 /cm**2.Comment: AJ in press Jan 2001, 14 pages plus 6 figures (but Fig. 1 has 4 separate parts, a through d). Data are available at http://adil.ncsa.uiuc.edu/document/00.HD.0

Laser pulse detection method and apparatus

A sensor is described for detecting the difference in phase of a pair of returned light pulse components, such as two components of a light pulse of an optical gyro. In an optic gyro, the two light components have passed in opposite directions through a coil of optical fiber, with the difference in phase of the returned light components determining the intensity of light shining on the sensor. The sensor includes a CCD (charge coupled device) that receives the pair of returned light components to generate a charge proportional to the number of photons in the received light. The amount of the charge represents the phase difference between the two light components. At a time after the transmission of the light pulse and before the expected time of arrival of the interfering light components, charge accumulating in the CCD as a result of reflections from components in the system, are repeatedly removed from the CCD, by transferring out charges in the CCD and dumping these charges

Radio Recombination Lines from Starbursts: NGC 3256, NGC 4945 and the Circinus Galaxy

A renewed attempt to detect radio recombination lines from external galaxies has resulted in the measurement of lines from several bright starburst galaxies. The lines are produced by hydrogen ionized by young, high-mass stars and are diagnostic of the conditions and gas dynamics in the starburst regions without problems of dust obscuration. We present here detections of the lines H91alpha and H92alpha near 8.6 GHz from the starburst nuclei in NGC 3256, NGC 4945, and the Circinus galaxy using the ATCA and VLA. Modelling the line emitting region as a collection of H II regions, we derive the required number of H II regions, their temperature, density, and distribution.Comment: 6 pages, to appear in "Proc 331. Heraeus Seminar: The Evolution of Starbursts", Bad Honnef, Germany, Aug 16 - 20, 2004, Eds: S. Huettemeister, S. Aalto, D.J. Bomans, and E. Manthe

Closed loop fiber optic rotation sensor

An improved optical gyroscope is provided, of the type that passes two light components in opposite directions through an optic fiber coil, and which adds a small variable frequency to one of the light components to cancel the phase shift due to rotation of the coil. The amount of coil rotation from an initial orientation, is accurately determined by combining the two light components, one of which has a slightly increased frequency, to develop beats that each represent a predetermined angle of rotation. The direction of rotation is obtained by combining the two light components on a photodetector, intermittently phase shifting a single light component by 90 deg and comparing the direction of change of photodetector output (+ or -) caused by the 90 deg shift, with the slope (+ or -) of the photodetector output at about the same time, when there is a 90 deg shift