2,745 research outputs found
Testing the Invariance of Cooling Rate in Gamma-Ray Burst Pulses
Recent studies have found that the spectral evolution of pulses within
gamma-ray bursts (GRBs) is consistent with simple radiative cooling. Perhaps
more interesting was a report that some bursts may have a single cooling rate
for the multiple pulses that occur within it. We determine the probability that
the observed "cooling rate invariance" is purely coincidental by sampling
values from the observed distribution of cooling rates. We find a 0.1-26%
probability that we would randomly observe a similar degree of invariance based
on a variety of pulse selection methods and pulse comparison statistics. This
probability is sufficiently high to warrant skepticism of any intrinsic
invariance in the cooling rate.Comment: 4 pages, 1 figure, to appear in Proceedings of the Fourth Huntsville
Symposium on Gamma-Ray Burst
Confronting Synchrotron Shock and Inverse Comptonization Models with GRB Spectral Evolution
The time-resolved spectra of gamma-ray bursts (GRBs) remain in conflict with
many proposed models for these events. After proving that most of the bursts in
our sample show evidence for spectral "shape-shifting", we discuss what
restrictions that BATSE time-resolved burst spectra place on current models. We
find that the synchrotron shock model does not allow for the steep low-energy
spectral slope observed in many bursts, including GRB 970111. We also determine
that saturated Comptonization with only Thomson thinning fails to explain the
observed rise and fall of the low-energy spectral slope seen in GRB 970111 and
other bursts. This implies that saturated Comptonization models must include
some mechanism which can cause the Thomson depth to increase intially in
pulses.Comment: (5 pages, 3 figures, to appear in Proceedings of the Fourth
Huntsville Symposium on Gamma-Ray Bursts
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Breast cancer tumour detection using microwave radar techniques
A breast cancer detection technique using multi-static radar is proposed herein. Images of a breast tumour are produced using this technique, with backscatter data. A wideband antenna design suitable for a breast cancer detection system is also described. Practical measurements are performed using a network analyser and a pair of antennas that are used to simulate an array. These initial images demonstrate the successful detection of a tumour phantom immersed in a liquid phantom with similar dielectric properties as the breast tissues
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Breast tumour detection using a flat 16 element array
A new experimental prototype of a breast cancer detection technique using real aperture multi-static radar is presented. The system comprises a fully-populated 16 element flat array and an associated system to switch between different transmit and receive elements. 3D images are produced using backscatter signals from a synthetic breast phantom. After suppression of skin reflections, initial images demonstrate the successful detection of 4-mmdiameter tumours
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Wideband microstrip patch antenna design for breast cancer tumour detection
A patch antenna is presented which has been designed to radiate into human breast tissue. The antenna is shown by means of simulation and practical measurement to possess a wide input bandwidth, stable radiation patterns and a good front-to-back ratio. Consideration is also given to its ability to radiate a pulse, and in this respect it is also found to be suitable for the proposed application
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Microwave detection of breast tumours
Copyright @ 2003 European Bioelectromagnetics Association
Numerical analysis of microwave detection of breast tumours using synthetic focussing techniques
Microwave detection of breast tumours is a non-ionising and potentially low-cost and more certain alternative to X-ray mammography. Analogous to ground penetrating radar (GPR), microwaves are transmitted using an antenna array and the reflected signals, which contain reflections from tumours, are recorded. The work presented here employs a post reception synthetically focussed detection method developed for land mine detection (R. Benjamin et al., IEE Proc. Radar, Sonar and Nav., vol. 148, no.4, pp. 233-40, 2001); all elements of an antenna array transmit a broadband signal in turn, the elements sharing a field of view with the current transmit element then record the received signal. By predicting the path delay between transmit and receive antennas via any desired point in the breast, it is then possible to extract and time-align all signals from that point. Repeated for all points in the breast, this yields an image in which the distinct dielectric properties of malignant tissue are potentially visible. This contribution presents a theoretical evaluation of the breast imaging system using FDTD methods. The FDTD model realistically models a practical system incorporating wide band antenna elements. One major challenge in breast cancer detection using microwaves is the clutter arising from skin interface. Deeply located tumours can be detected using windowing techniques (R. Nilavalan et al., Electronics Letters, vol. 39, pp. 1787-1789, 2003); however tumours closer to the skin interface require additional consideration, as described herein
On the Hardness-Intensity Correlation in Gamma-Ray Burst Pulses
We study the hardness-intensity correlation (HIC) in gamma-ray bursts (GRBs).
In particular, we analyze the decay phase of pulse structures in their light
curves. The study comprises a sample of 82 long pulses selected from 66 long
bursts observed by BATSE on the Compton Gamma-Ray Observatory. We find that at
least 57% of these pulses have HICs that can be well described by a power law.
The distribution of the power law indices, obtained by modeling the HIC of
pulses from different bursts, is broad with a mean of 1.9 and a standard
deviation of 0.7. We also compare indices among pulses from the same bursts and
find that their distribution is significantly narrower. The probability of a
random coincidence is shown to be very small. In most cases, the indices are
equal to within the uncertainties. This is particularly relevant when comparing
the external versus the internal shock models. In our analysis, we also use a
new method for studying the HIC, in which the intensity is represented by the
peak value of the E F_E spectrum. This new method gives stronger correlations
and is useful in the study of various aspects of the HIC. In particular, it
produces a better agreement between indices of different pulses within the same
burst. Also, we find that some pulses exhibit a "track jump" in their HICs, in
which the correlation jumps between two power laws with the same index. We
discuss the possibility that the "track jump" is caused by strongly overlapping
pulses. Based on our findings, the constancy of the index is proposed to be
used as a tool for pulse identification in overlapping pulses.Comment: 20 pages with 9 eps figures (emulateapj), ApJ accepte
Multilingual gendered identities: female undergraduate students in London talk about heritage languages
In this paper I explore how a group of female university students, mostly British Asian and in their late teens and early twenties, perform femininities in talk about heritage languages. I argue that analysis of this talk reveals ways in which the participants enact âculturally intelligibleâ gendered subject positions. This frequently involves negotiating the norms of âheteronormativityâ, constituting femininity in terms of marriage, motherhood and maintenance of heritage culture and language, and âgirl powerâ, constituting femininity in terms of youth, sassiness, glamour and individualism. For these young women, I ask whether higher education can become a site in which they have the opportunities to explore these identifications and examine other ways of imagining the self and what their stories suggest about âdoing beingâ a young British Asian woman in London
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Experimental investigation of real aperture synthetically organised radar for breast cancer detection
Breast cancer is the most common cancer in woman, and early detection increases the likelihood of successful treatment and long-term survival screen film mammography is currently the most effective method for detecting breast tumours, however this technique suffers from relatively high false negative and positive detection rates, and it involves uncomfortable compression of the breast. This paper presents the experimental investigation of real aperture synthetically organised radar for breast cancer detection. The work presented herein originated as a theoretical study employing FDTD models. This contribution presents subsequent experimental validation using a mechanically-scanned 2 element antenna array and a breast phantom consisting of synthetic biological materials
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