73 research outputs found
Conjugate two-dimensional electric potential maps
Two dimensional electric potential maps based on voltage detection in
conducting paper are common practice in many physics courses in college. Most
frequently, students work on `capacitor-like' geometries with current flowing
between two opposite electrodes. A `topographical' investigation across the
embedding medium (map of equipotential curves) allows to reassure a number of
physical properties.
This paper focuses on some less common configurations that bear pedagogical
interest. We analyze `open-geometries' with electrodes in the form of long
strips with slits. They provide a natural groundwork to bring the student to
complex variable methods. Aided by this, we show that shaping the conducting
paper board one may analyze finite size effects, as well as some meaningful
discontinuities in the measured potential.
The concept of conjugate electric potentials is exploited. Equipotentials and
electric field lines acquire interchangeable roles and may be obtained in
complementary `dual' experiments. A feasible theoretical analysis based on
introductory complex variables and standardized numerics gives a remarkable
quantification of the experimental results.Comment: 15 pages, 8 figure
Prevalence of congenital coronary artery anomalies and variants in 726 consecutive patients based on 64-slice coronary computed tomography angiography
Background: Coronary computed tomography angiography (CCTA) is helpful in making a precise noninvasive evaluation of coronary anatomy, allowing concomitant evaluation of other cardiac structures. The aim of this study was to determine the prevalence of coronary artery variations detected by 64-slice mutidetector CT.
Materials and methods: The results of ECG-gated CCTA in 726 consecutive patients (mean age 58 years) were analysed retrospectively. The main indicationsfor CCTA were a typical chest pain, angina pectoris, screening for coronary artery disease and determination of the patency of bypass grafts or stents. Acquisitionwas performed with a 64-detector CT scanner with retrospective ECG gating. Imaging results were assessed by experienced cardiovascular radiologist.
Results: The overall incidence of coronary artery anomalies was 1.1% (8 out of 726 participants). The most common anomaly was an anomalous origin of the circumflex artery from the right coronary sinus with a retroaortic course (4 patients,0.6%), followed by origin of right coronary artery from the left coronary sinus (2 patients, 0.3%). One patient with abnormal origin of the left main artery from the right coronary sinus (0.1%) and 1 patient with a circumflex artery origin from the proximal segment of the right coronary artery (0.1%) were observed, both with retroartic course.
Conclusions: CCTA is a noninvasive imaging technique useful for the precise evaluation of variations of the coronary arteries. This study shows similar results to other reports on this subject.
Persistent left superior vena cava with an absent right superior vena cava in a 72-year-old male with multivessel coronary artery disease
Congenital anomalies of systemic veins are usually asymptomatic and foundincidentally during ultrasonography, computed tomography (CT) or magneticresonance examinations performed for other clinical indications. Persistent leftsuperior vena cava (PLSVC) with absent right superior vena cava (RSVC) is thecongenital aberration in the thoracic venous system which occurs in only 0.09%to 0.13% of patients who have congenital heart defects. In this paper, we presentthe extremely rare case of a 72-year-old male with PLSVC associated withan absence of RSVC, referred for coronary CT angiography. Multidetector CTangiography is a powerful tool for the detection of venous anomalies, which isessential before invasive procedures such as the implantation of pacemakers
New detectors for the kaon and hypernuclear experiments with KaoS at MAMI and with PANDA at GSI
The KaoS spectrometer at the Mainz Microtron MAMI, Germany, is perceived as
the ideal candidate for a dedicated spectrometer in kaon and hypernuclei
electroproduction. KaoS will be equipped with new read-out electronics, a
completely new focal plane detector package consisting of scintillating fibres,
and a new trigger system. First prototypes of the fibre detectors and the
associated new front-end electronics are shown in this contribution. The Mainz
hypernuclei research program will complement the hypernuclear experiments at
the planned FAIR facility at GSI, Germany. At the proposed antiproton storage
ring the spectroscopy of double Lambda hypernuclei is one of the four main
topics which will be addressed by the PANDA Collaboration. The experiments
require the operation of high purity germanium (HPGe) detectors in high
magnetic fields (B= 1T) in the presence of a large hadronic background. The
performance of high resolution Ge detectors in such an environment has been
investigated.Comment: Presentation at International Symposium on the Development of
Detectors for Particle, Astroparticle and Synchrotron Radiation Experiments,
Stanford, Ca (SNIC06), 6 pages, LaTeX, 11 eps figure
Observation of Lambda H-4 hyperhydrogen by decay-pion spectroscopy in electron scattering
At the Mainz Microtron MAMI, the first high-resolution pion spectroscopy from
decays of strange systems was performed by electron scattering off a Be-9
target in order to study the ground-state masses of Lambda-hypernuclei.
Positively charged kaons were detected by a short-orbit spectrometer with a
broad momentum acceptance at zero degree forward angles with respect to the
beam, efficiently tagging the production of strangeness in the target nucleus.
In coincidence, negatively charged decay-pions were detected by two independent
high-resolution spectrometers. About 10^3 pionic weak decays of hyperfragments
and hyperons were observed. The pion momentum distribution shows a
monochromatic peak at p_pi ~ 133 MeV/c, corresponding to the unique signature
for the two-body decay of hyperhydrogen Lambda H-4 -> He-4 + pi-, stopped
inside the target. Its binding energy was determined to be B_Lambda = 2.12 +-
0.01 (stat.) +- 0.09 (syst.) MeV with respect to the H-3 + Lambda mass
Exclusive electroproduction of K+ Lambda and K+ Sigma^0 final states at Q^2 = 0.030-0.055 (GeV/c)^2
Cross section measurements of the exclusive p(e,e'K+)Lambda,Sigma^0
electroproduction reactions have been performed at the Mainz Microtron MAMI in
the A1 spectrometer facility using for the first time the Kaos spectrometer for
kaon detection. These processes were studied in a kinematical region not
covered by any previous experiment. The nucleon was probed in its third
resonance region with virtual photons of low four-momenta, Q^2= 0.030-0.055
(GeV/c)^2. The MAMI data indicate a smooth transition in Q^2 from
photoproduction to electroproduction cross sections. Comparison with
predictions of effective Lagrangian models based on the isobar approach reveal
that strong longitudinal couplings of the virtual photon to the N* resonances
can be excluded from these models.Comment: 16 pages, 7 figure
Metabolic profiling of human brain metastases using in vivo proton MR spectroscopy at 3T
<p>Abstract</p> <p>Background</p> <p>Metastases to the central nervous system from different primary cancers are an oncologic challenge as the overall prognosis for these patients is generally poor. The incidence of brain metastases varies with type of primary cancer and is probably increasing due to improved therapies of extracranial metastases prolonging patient's overall survival and thereby time for brain metastases to develop. In addition, the greater access to improved neuroimaging techniques can provide earlier diagnosis. The aim of this study was to investigate the feasibility of using proton magnetic resonance spectroscopy (MRS) and multivariate analyses to characterize brain metastases originating from different primary cancers, to assess changes in spectra during radiation treatment and to correlate the spectra to clinical outcome after treatment.</p> <p>Methods</p> <p>Patients (n = 26) with brain metastases were examined using single voxel MRS at a 3T clinical MR system. Five patients were excluded due to poor spectral quality. The spectra were obtained before start (n = 21 patients), immediately after (n = 6 patients) and two months after end of treatment (n = 4 patients). Principal component analysis (PCA) and partial least square regression analysis (PLS) were applied in order to identify clustering of spectra due to origin of metastases and to relate clinical outcome (survival) of the patients to spectral data from the first MR examination.</p> <p>Results</p> <p>The PCA results indicated that brain metastases from primary lung and breast cancer were separated into two clusters, while the metastases from malignant melanomas showed no uniformity. The PLS analysis showed a significant correlation between MR spectral data and survival five months after MRS before start of treatment.</p> <p>Conclusion</p> <p>MRS determined metabolic profiles analysed by PCA and PLS might give valuable clinical information when planning and evaluating the treatment of brain metastases, and also when deciding to terminate further therapies.</p
A new measurement of the structure functions and in virtual Compton scattering at 0.33 (GeV/c)
The cross section of the reaction has been measured at
(GeV/c). The experiment was performed using the electron beam
of the MAMI accelerator and the standard detector setup of the A1
Collaboration. The cross section is analyzed using the low-energy theorem for
virtual Compton scattering, yielding a new determination of the two structure
functions P_LL}-P_{TT}/epsilon and which are linear combinations of
the generalized polarizabilities of the proton. We find somewhat larger values
than in the previous investigation at the same . This difference, however,
is purely due to our more refined analysis of the data. The results tend to
confirm the non-trivial -evolution of the generalized polarizabilities and
call for more measurements in the low- region ( 1 (GeV/c)).Comment: 9 pages, 10 figures. EPJA version. slight revisions in the text and
figure
Beam-helicity asymmetry in photon and pion electroproduction in the Delta(1232) resonance region at Q^2= 0.35 (GeV/c)^2
The beam-helicity asymmetry has been measured simultaneously for the
reactions (e p \to e p \gamma) and (e p \to e p \pi^0) in the
resonance region at 0.35 (GeV/c). The experiment was performed at
MAMI with a longitudinally polarized beam and an out-of-plane detection of the
proton. The results are compared with calculations based on Dispersion
Relations for virtual Compton scattering and with the MAID model for pion
electroproduction. There is an overall good agreement between experiment and
theoretical calculations. The remaining discrepancies may be ascribed to an
imperfect parametrization of some multipoles, mainly
contributing to the non-resonant background. The beam-helicity asymmetry in
both channels ( and ) shows a good sensitivity to these
multipoles and should allow future improvement in their parametrization.Comment: 7 pages, 8 figures, version to appear in EPJ
Inverted stress- induced cardiomyopathy as a unusual variant of acute heart failure after cesarean delivery- a case report
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