367 research outputs found
Beam Based Alignment of Interaction Region Magnets
In conventional beam based alignment (BBA) procedures, the relative alignment
of a quadrupole to a nearby beam position monitor is determined by finding a
beam position in the quadrupole at which the closed orbit does not change when
the quadrupole field is varied. The final focus magnets of the interaction
regions (IR) of circular colliders often have some specialized properties that
make it difficult to perform conventional beam based alignment procedures. At
the HERA interaction points, for example, these properties are: (a) The
quadrupoles are quite strong and long. Therefore a thin lens approximation is
quite imprecise. (b) The effects of angular magnet offsets become significant.
(c) The possibilities to steer the beam are limited as long as the alignment is
not within specifications. (d) The beam orbit has design offsets and design
angles with respect to the axis of the low-beta quadrupoles. (e) Often
quadrupoles do not have a beam position monitor in their vicinity. Here we
present a beam based alignment procedure that determines the relative offset of
the closed orbit from a quadrupole center without requiring large orbit changes
or monitors next to the quadrupole. Taking into account the alignment angle
allows us to reduce the sensitivity to optical errors by one to two orders of
magnitude. We also show how the BBA measurements of all IR quadrupoles can be
used to determine the global position of the magnets. The sensitivity to errors
of this method is evaluated and its applicability to HERA is shown
How to Commission, Operate and Maintain a Large Future Accelerator Complex from Far Remote
A study on future large accelerators [1] has considered a facility, which is
designed, built and operated by a worldwide collaboration of equal partner
institutions, and which is remote from most of these institutions. The full
range of operation was considered including commi-ssioning, machine
development, maintenance, trouble shooting and repair. Experience from existing
accele-rators confirms that most of these activities are already performed
'remotely'. The large high-energy physics ex-periments and astronomy projects,
already involve inter-national collaborations of distant institutions. Based on
this experience, the prospects for a machine operated remotely from far sites
are encouraging. Experts from each laboratory would remain at their home
institution but continue to participate in the operation of the machine after
construction. Experts are required to be on site only during initial
commissioning and for par-ticularly difficult problems. Repairs require an
on-site non-expert maintenance crew. Most of the interventions can be made
without an expert and many of the rest resolved with remote assistance. There
appears to be no technical obstacle to controlling an accelerator from a
distance. The major challenge is to solve the complex management and
communication problems.Comment: ICALEPCS 2001 abstract ID No. FRBI001 invited talk submitting author
F. Willeke 5 pages, 1 figur
Stress-Induced Allodynia – Evidence of Increased Pain Sensitivity in Healthy Humans and Patients with Chronic Pain after Experimentally Induced Psychosocial Stress
Background: Experimental stress has been shown to have analgesic as well as allodynic effect in animals. Despite the obvious negative influence of stress in clinical pain conditions, stress-induced alteration of pain sensitivity has not been tested in humans so far. Therefore, we tested changes of pain sensitivity using an experimental stressor in ten female healthy subjects and 13 female patients with fibromyalgia. Methods: Multiple sensory aspects of pain were evaluated in all participants with the help of the quantitative sensory testing protocol before (60 min) and after (10 and 90 min) inducing psychological stress with a standardized psychosocial stress test (“Trier Social Stress Test”). Results: Both healthy subjects and patients with fibromyalgia showed stress-induced enhancement of pain sensitivity in response to thermal stimuli. However, only patients showed increased sensitivity in response to pressure pain. Conclusions: Our results provide evidence for stress-induced allodynia/hyperalgesia in humans for the first time and suggest differential underlying mechanisms determining response to stressors in healthy subjects and patients suffering from chronic pain. Possible mechanisms of the interplay of stress and mediating factors (e.g. cytokines, cortisol) on pain sensitivity are mentioned. Future studies should help understand better how stress impacts on chronic pain conditions
Clinical Characteristics of Cutaneous Melanoma and Second Primary Malignancies in a Dutch Hospital-Based Cohort of Cutaneous Melanoma Patients
The increasing number of living cutaneous melanoma patients and the increased risk of developing a second primary tumour incited us to analyse the clinical characteristics of cutaneous melanoma and define the frequency, site, and type of second primary cancers in cutaneous melanoma patients. We collected data on patients who visited the Department of Dermatology at the Radboud University Nijmegen Medical Centre and were newly diagnosed with cutaneous melanoma or metastasis of melanoma with unknown primary localization between 2002 and 2006. A total of 194 cases were included; eleven patients developed a subsequent melanoma, 24 had at least one basal cell carcinoma, three had at least one squamous cell carcinoma, and 21 patients had a second non-cutaneous primary malignancy. In conclusion, 48 patients developed a subsequent malignancy. As nonmelanoma skin cancer is the most frequent second malignancy, our results subscribe to the necessity of follow-up by a dermatologist
Detecting chaos in particle accelerators through the frequency map analysis method
The motion of beams in particle accelerators is dominated by a plethora of
non-linear effects which can enhance chaotic motion and limit their
performance. The application of advanced non-linear dynamics methods for
detecting and correcting these effects and thereby increasing the region of
beam stability plays an essential role during the accelerator design phase but
also their operation. After describing the nature of non-linear effects and
their impact on performance parameters of different particle accelerator
categories, the theory of non-linear particle motion is outlined. The recent
developments on the methods employed for the analysis of chaotic beam motion
are detailed. In particular, the ability of the frequency map analysis method
to detect chaotic motion and guide the correction of non-linear effects is
demonstrated in particle tracking simulations but also experimental data.Comment: Submitted for publication in Chaos, Focus Issue: Chaos Detection
Methods and Predictabilit
Acute neuropsychiatry:a confused patient and a puzzled doctor
BACKGROUND: Anti-NMDA-receptor-encephalitis is a progressive autoimmune disease with significant mortality if left untreated.CASE DESCRIPTION: A 58-year-old man without previous psychiatric or neurologic history presented at the emergency department after brief loss of consciousness at work. Within a few hours, the patient developed acute neuropsychiatric symptoms, including altered levels of consciousness, aggression, incoherence, change in behaviour, and psychomotor agitation. Initially, additional blood, cerebrospinal fluid and EEG tests showed no abnormalities. Over the course of the following days, catatonia, orofacial dyskinesia and autonomic-function disorder developed, eventually with respiratory insufficiency, necessitating transfer to the intensive-care unit. At this stage, the EEG did show abnormalities, and cerebrospinal fluid analysis showed marginal pleocytosis. The patient was treated with intravenous methylprednisolone and immunoglobins. Anti-NMDA-receptor antibodies were present in the blood and cerebrospinal fluid. Screening for malignancy identified small-cell lung carcinoma, for which the patient was treated with cytostatic agents.CONCLUSION: Acute neuropsychiatric symptoms in a middle-aged patient with no psychiatric medical history are suggestive of an underlying somatic cause. Timely recognition and treatment of anti-NMDA-receptor encephalitis is essential to improve the prognosis.</p
Spectral analysis and resolving spatial ambiguities in human sound localization
This dissertation provides an overview of my research over the last five years into the spectral analysis involved in human sound localization. The work involved conducting psychophysical tests of human auditory localization performance and then applying analytical techniques to analyze and explain the data. It is a fundamental thesis of this work that human auditory localization response directions are primarily driven by the auditory localization cues associated with the acoustic filtering properties of the external auditory periphery, i.e., the head, torso, shoulder, neck, and external ears. This work can be considered as composed of three parts. In the first part of this work, I compared the auditory localization performance of a human subject and a time-delay neural network model under three sound conditions: broadband, high-pass, and low-pass. A “black-box” modeling paradigm was applied. The modeling results indicated that training the network to localize sounds of varying center-frequency and bandwidth could degrade localization performance results in a manner demonstrating some similarity to human auditory localization performance. As the data collected during the network modeling showed that humans demonstrate striking localization errors when tested using bandlimited sound stimuli, the second part of this work focused on human sound localization of bandpass filtered noise stimuli. Localization data was collected from 5 subjects and for 7 sound conditions: 300 Hz to 5 kHz, 300 Hz to 7 kHz, 300 Hz to 10 kHz, 300 Hz to 14 kHz, 3 to 8 kHz, 4 to 9 kHz, and 7 to 14 kHz. The localization results were analyzed using the method of cue similarity indices developed by Middlebrooks (1992). The data indicated that the energy level in relatively wide frequency bands could be driving the localization response directions, just as in Butler’s covert peak area model (see Butler and Musicant, 1993). The question was then raised as to whether the energy levels in the various frequency bands, as described above, are most likely analyzed by the human auditory localization system on a monaural or an interaural basis. In the third part of this work, an experiment was conducted using virtual auditory space sound stimuli in which the monaural spectral cues for auditory localization were disrupted, but the interaural spectral difference cue was preserved. The results from this work showed that the human auditory localization system relies primarily on a monaural analysis of spectral shape information for its discrimination of directions on the cone of confusion. The work described in the three parts lead to the suggestion that a spectral contrast model based on overlapping frequency bands of varying bandwidth and perhaps multiple frequency scales can provide a reasonable algorithm for explaining much of the current psychophysical and neurophysiological data related to human auditory localization
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