594 research outputs found
Superintegrable Hamiltonian systems with noncompact invariant submanifolds. Kepler system
The Mishchenko-Fomenko theorem on superintegrable Hamiltonian systems is
generalized to superintegrable Hamiltonian systems with noncompact invariant
submanifolds. It is formulated in the case of globally superintegrable
Hamiltonian systems which admit global generalized action-angle coordinates.
The well known Kepler system falls into two different globally superintegrable
systems with compact and noncompact invariant submanifolds.Comment: 23 page
Geometrical aspects of integrable systems
We review some basic theorems on integrability of Hamiltonian systems, namely
the Liouville-Arnold theorem on complete integrability, the Nekhoroshev theorem
on partial integrability and the Mishchenko-Fomenko theorem on noncommutative
integrability, and for each of them we give a version suitable for the
noncompact case. We give a possible global version of the previous local
results, under certain topological hypotheses on the base space. It turns out
that locally affine structures arise naturally in this setting.Comment: It will appear on International Journal of Geometric Methods in
Modern Physics vol.5 n.3 (May 2008) issu
Flux creep in Bi2Sr2CaCu2O8(sub +x) single crystals
The results of a magnetic study on a Bi2Sr2CaCu2O(8+x) single crystal are reported. Low field susceptibility (dc and ac), magnetization cycles and time dependent measurements were performed. With increasing the temperature the irreversible regime of the magnetization cycles is rapidly restricted to low fields, showing that the critical current J(sub c) becomes strongly field dependent well below T(sub c). At 2.4 K the critical current in zero field, determined from the remanent magnetization by using the Bean formula for the critical state, is J(sub c) = 2 10(exp 5) A/sq cm. The temperature dependence of J(sub c) is satisfactorily described by the phenomenological law J(sub c) = J(sub c) (0) (1 - T/T(sub c) (sup n), with n = 8. The time decay of the zero field cooled magnetization and of the remanent magnetization was studied at different temperatures for different magnetic fields. The time decay was found to be logarithmic in both cases, at least at low temperatures. At T = 4.2 K for a field of 10 kOe applied parallel to the c axis, the average pinning energy, determined by using the flux creep model, is U(sub o) = 0.010 eV
Assessment of Identity Disturbance: Factor Structure and Validation of the Personality Structure Questionnaire in an Italian Sample
here are few brief measures of identity disturbance for use in clinical
practice
that have
been subject to any cross
-
culturally validation
. This study investigated the construct
validity of the Personality Structure Questionnaire (PSQ)
in Italian
clinical (N=237) and
community (
N=296) samples
. Confirmatory factor analysis was conducted to
investigate the internal structure of the PSQ. A three
–
factor structure (i.e., differing self
-
states, mood variability and behavioral loss of control) including
a second
-
order factor
provided the best fit to the data
. This structure was
demonstrated to be invariant across
sex
and
clinical
diagnosis
, with clinical diagnosis significantly predicting increased
PSQ
scores
.
A g
lobal
PSQ score
of
between 26
-
28 was found to be an appropriate cut-off for
assisting in diagnostic processes. Implications for the assessment and treatment of
psychological disorders with a marked identity disturbance component are discussed
Global action-angle coordinates for completely integrable systems with noncompact invariant submanifolds
The obstruction to the existence of global action-angle coordinates of
Abelian and noncommutative (non-Abelian) completely integrable systems with
compact invariant submanifolds has been studied. We extend this analysis to the
case of noncompact invariant submanifolds.Comment: 13 pages, to be published in J. Math. Phys. (2007
Exchange bias effect in the phase separated Nd_{1-x}Sr_{x}CoO_3 at the spontaneous ferromagnetic/ferrimagnetic interface
We report the new results of exchange bias effect in Nd_{1-x}Sr_{x}CoO_3 for
x = 0.20 and 0.40, where the exchange bias phenomenon is involved with the
ferrimagnetic (FI) state in a spontaneously phase separated system. The
zero-field cooled magnetization exhibits the FI (T_{FI}) and ferromagnetic
(T_C) transitions at ~ 23 and \sim 70 K, respectively for x = 0.20. The
negative horizontal and positive vertical shifts of the magnetic hysteresis
loops are observed when the system is cooled through T_{FI} in presence of a
positive static magnetic field. Training effect is observed for x = 0.20, which
could be interpreted by a spin configurational relaxation model. The
unidirectional shifts of the hysteresis loops as a function of temperature
exhibit the absence of exchange bias above T_{FI} for x = 0.20. The analysis of
the cooling field dependence of exchange bias field and magnetization indicates
that the ferromagnetic (FM) clusters consist of single magnetic domain with
average size around \sim 20 and ~ 40 \AA ~ for x = 0.20 and 0.40, respectively.
The sizes of the FM clusters are close to the percolation threshold for x =
0.20, which grow and coalesce to form the bigger size for x = 0.40 resulting in
a weak exchange bias effect.Comment: 9 pages, 9 figure
Laser remote sensing calibration of ocean color satellite data
world ocean: in fact, those processes dramatically affect the climatic equilibrium of our planet. For this reason,
many advanced active and passive remote sensors have been used to study phytoplankton dynamics, since such
phenomena are thought to be responsible for the sequestration of atmospheric carbon dioxide, one of the most
important greenhouse gases. In this paper, one laser system and three satellite radiometers routinely used for the
study of the phytoplankton dynamics will be briefly reviewed. Satellite sensors have been preferred to airborne
sensors because, to our knowledge, ocean color airborne radiometers have not been operated in Antarctica, at
least not throughout the whole lapse of time examined in this study. Particular focus was on the laser system
(ELF) and on a specific satellite radiometer (SeaWiFS). ELF is based on the laser-induced fluorescence of phytoplankton
pigments and was conceived for the Italian expeditions to Antarctica. The goal of SeaWiFS is to provide
the Earth science community with quantitative data on the global ocean bio-optical properties. Such satellite
radiometer has been calibrated with in situ data mainly acquired in non polar regions. This is why a comparison
between ELF and SeaWiFS measurements of chlorophyll-a surface concentrations in the Southern Ocean
during the austral summer 1997-1998 was believed to be significant. Our results indicate that SeaWiFS overestimates
high concentrations and underestimates low concentrations. In order to correct this behavior, the chlorophyll-
a bio-optical algorithm of SeaWiFS has been recalibrated according to the measurements of ELF, thus providing
a new estimation of the primary production in the Southern Ocean
Re-entrant spin glass and magnetoresistance in Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide
We have investigated the static and dynamic response of magnetic clusters in
Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide, where a sequence of magnetic
phase transitions, i.e., paramagnetic (PM) to ferromagnetic at T_{C}
270K and ferromagnetic to canted spin glass state at T_f\leq$ 125K is
observed
Magnetic properties of the frustrated AFM spinel ZnCr_2O_4 and the spin-glass Zn_{1-x}Cd_xCr_2O_4 (x=0.05,0.10)
The -dependence (2- 400 K) of the electron paramagnetic resonance (EPR),
magnetic susceptibility, , and specific heat, , of the
antiferromagnetic (AFM) spinel ZnCrO and the spin-glass
(SG) ZnCdCrO () is reported. These
systems behave as a strongly frustrated AFM and SG with K and -400 K K. At high-
the EPR intensity follows the and the -value is -independent.
The linewidth broadens as the temperature is lowered, suggesting the existence
of short range AFM correlations in the paramagnetic phase. For
ZnCrO the EPR intensity and decreases below 90 K and 50
K, respectively. These results are discussed in terms of nearest-neighbor
Cr (S %) spin-coupled pairs with an exchange coupling of 50 K. The appearance of small resonance modes for K,
the observation of a sharp drop in and a strong peak in
at K confirms, as previously reported, the existence of long range
AFM correlations in the low- phase. A comparison with recent neutron
diffraction experiments that found a near dispersionless excitation at 4.5 meV
for and a continuous gapless spectrum for ,
is also given.Comment: 17 pages, 8 figures, 1 Table. Submitted to Physical Review
Ambulatory surgery for perianal Crohn’s disease. Study of feasibility
Background. One-third of Crohn’s disease (CD) patients present perianal fistula. The gold standard in the diagnosis and treatment of symptomatic perianal disease (PAD) in CD is the exploration of the anal canal and distal rectum under anesthesia (EUA). This procedure is mainly conducted as a day case surgery. Unfortunately, it is not always possible to proceed within the ideal timing and any delay may well represent a relevant clinical issue. The aim of this study was to evaluate the feasibility of outpatient treatment of symptomatic perianal fistulas in CD patients. Methods. All CD patients under regular follow-up at our inflammatory bowel disease referral center, presenting with symptomatic perianal fistulas, were offered surgical consultation. The data of patients were prospectively collected for three years (February 2014 to February 2017) for the purpose of the study. All clinical information, including previous EUA and/or records from MRI and endoscopic ultrasound, was included. Outpatient anal canal and distal rectum exploration and treatment (OE) were undertaken during the specialist surgical consultation. Fistulas were classified according to Parks’s classification; the type of outpatient treatment and compliance of patients were recorded. Pain was assessed by VAS at the time of the procedure and during the first control. Patients were followed up in the surgical clinic in relation to the study. Results. Ninety-two CD patients with symptomatic perianal fistulas had surgical consultation during the study period. OE was offered to all but 18 patients who fulfilled the exclusion criteria or had an extremely severe disease; six patients refused the OE (8.11%). Of the 68 patients undergoing OE, eleven (16.18%) had previous surgery for perianal disease. The OE was accomplished in sixty-one patients (89.71%), while in 7 patients, it was abandoned for scarce compliance. Nine patients (14.75%) underwent drainage of perianal abscess; in 3 of them, it was possible to probe the fistula tract, find the internal orifice, and pass a loose seton. Overall, setonage was performed in 50 patients (81.97%). Rectovaginal setons were placed in 3 patients and more than one seton (up to 3) in 6 cases. Fistulotomy was performed in 4 simple subcutaneous fistulous tracts. Concordance with the preoperative findings was found in 54 out of 61 patients. EUA was scheduled at the time of OE for the 7 patients who did not complete the procedure. All sixty-one patients who had the OE were followed up for a minimum of 12 months. Conclusions. This preliminary study indicates that OE in CD patients with symptomatic perianal fistulas is safe and feasible in a high-volume referral center. It might provide several benefits, including patients’ logistics, reduce or remove patients’ symptoms and discomfort, allow for a timely start of medical therapy, and avoid further complications
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