687 research outputs found
Theory of the Trojan-Horse Method
The Trojan-Horse method is an indirect approach to determine the energy
dependence of S-factors of astrophysically relevant two-body reactions. This is
accomplished by studying closely related three-body reactions under quasi-free
scattering conditions. The basic theory of the Trojan-Horse method is developed
starting from a post-form distorted wave Born approximation of the T-matrix
element. In the surface approximation the cross section of the three-body
reaction can be related to the S-matrix elements of the two-body reaction. The
essential feature of the Trojan-Horse method is the effective suppression of
the Coulomb barrier at low energies for the astrophysical reaction leading to
finite cross sections at the threshold of the two-body reaction. In a modified
plane wave approximation the relation between the two-body and three-body cross
sections becomes very transparent. The appearing Trojan-Horse integrals are
studied in detail.Comment: 27 pages, REVTeX4, 4 figures, 1 tabl
Indirect techniques in nuclear astrophysics. Asymptotic Normalization Coefficient and Trojan Horse
Owing to the presence of the Coulomb barrier at astrophysically relevant
kinetic energies it is very difficult, or sometimes impossible, to measure
astrophysical reaction rates in the laboratory. That is why different indirect
techniques are being used along with direct measurements. Here we address two
important indirect techniques, the asymptotic normalization coefficient (ANC)
and the Trojan Horse (TH) methods. We discuss the application of the ANC
technique for calculation of the astrophysical processes in the presence of
subthreshold bound states, in particular, two different mechanisms are
discussed: direct capture to the subthreshold state and capture to the
low-lying bound states through the subthreshold state, which plays the role of
the subthreshold resonance. The ANC technique can also be used to determine the
interference sign of the resonant and nonresonant (direct) terms of the
reaction amplitude. The TH method is unique indirect technique allowing one to
measure astrophysical rearrangement reactions down to astrophysically relevant
energies. We explain why there is no Coulomb barrier in the sub-process
amplitudes extracted from the TH reaction. The expressions for the TH amplitude
for direct and resonant cases are presented.Comment: Invited talk on the Conference "Nuclear Physics in Astrophysics II",
Debrecen, Hungary, 16-20 May, 200
Atorvastatin combined to interferon to verify the efficacy (ACTIVE) in relapsing-remitting active multiple sclerosis patients: a longitudinal controlled trial of combination therapy.
A large body of evidence suggests that, besides their cholesterol-lowering effect, statins exert anti-inflammatory action. Consequently, statins may have therapeutic potential in immune-mediated disorders such as multiple sclerosis. Our objectives were to determine safety, tolerability and efficacy of low-dose atorvastatin plus high-dose interferon beta-1a in multiple sclerosis patients responding poorly to interferon beta-1a alone. Relapsingâremitting multiple sclerosis patients, aged 18â50 years, with contrast-enhanced lesions or relapses while on therapy with interferon beta-1a 44 mg (three times weekly) for 12 months, were randomized to combination therapy (interferon+atorvastatin 20mg per day; group A) or interferon alone (group B) for 24 months. Patients underwent blood analysis and clinical assessment with the Expanded Disability Status Scale every 3 months, and brain gadolinium-enhanced magnetic resonance imaging at screening, and 12 and 24 months thereafter. Primary outcome measure was contrast-enhanced lesion number. Secondary outcome measures were number of relapses, EDSS variation and safety laboratory data. Forty-five patients were randomized to group A (n 1â4 21) or B (n 1â4 24). At 24 months, group A had significantly fewer contrast-enhanced lesions versus baseline (p 1â4 0.007) and significantly fewer relapses versus the two pre-randomization years (p < 0.001). At survival analysis, the risk for a 1-point EDSS increase was slightly higher in group B than in group A (p 1â4 0.053). Low-dose atorvastatin may be beneficial, as add-on therapy, in poor responders to high-dose interferon beta-1a alone
Big Bang nucleosynthesis revisited via Trojan Horse Method measurements
Nuclear reaction rates are among the most important input for understanding
the primordial nucleosynthesis and therefore for a quantitative description of
the early Universe. An up-to-date compilation of direct cross sections of
2H(d,p)3H, 2H(d,n)3He, 7Li(p,alpha)4He and 3He(d,p)4He reactions is given.
These are among the most uncertain cross sections used and input for Big Bang
nucleosynthesis calculations. Their measurements through the Trojan Horse
Method (THM) are also reviewed and compared with direct data. The reaction
rates and the corresponding recommended errors in this work were used as input
for primordial nucleosynthesis calculations to evaluate their impact on the 2H,
3,4He and 7Li primordial abundances, which are then compared with observations.Comment: 22 pages, 7 figures, accepted for publication in The Astrophysical
Journa
West syndrome followed by juvenile myoclonic epilepsy: a coincidental occurrence?
West syndrome followed by juvenile
myoclonic epilepsy: a coincidental
occurrence? is an age-dependent epilepsy with onset peak in the first
year of life. According to the ILAE classification, the
etiology of WS could be symptomatic or cryptogenic. An
idiopathic etiology was considered too. In literature, there
was never previously described a transition from WS to
JME.
Methods: The proband, (male) was referred to our
Department at the age of 8 months because he showed
clusters of symmetric spasms. Interictal EEG recording
displayed an hypsarrhythmic pattern. The clinical and EEG
data suggested WS diagnosis. At 1 year of age increasing
long and thick hair in both elbow regions was observed.
This picture suggested an additional diagnosis of \u201cHairy
Elbows Syndrome\u201d. During follow-up, the neurological
examination was normal and the EEGs showed age
appropriate background activity without abnormalities until
12 years of age, when he experienced some clusters of
bilateral, arrhythmic myoclonic jerks, synchronous with
generalized discharges of 4Hz spike-wave. This features
suggested JME diagnosis.
Results: We report a child with WS with onset at 8 months
of age followed by JME at 12 years of age. This unusual
evolution, never reported previously, suggests that both
seizure types may share some pathophysiological processes
genetically determined, which produce a susceptibility to
seizure.
Conclusion: This case documents a new transition type
from WS to JME and improves the knowledge about the
spectrum of seizure susceptibility. These findings suggest
that some genes other than those currently known and nonconventional
genetic factors can play a role in seizure
predisposition
Migraine and Cranial Autonomic Symptoms in Children and Adolescents: A Clinical Study
The frequency of cranial autonomic symptoms in children affected by primary headaches is uncertain. The aim of our study was to estimate the frequency of symptoms in pediatric headaches and correlate it with main migraine characteristics. A questionnaire investigating the presence of cranial autonomic symptoms was administered to all children with primary headache for 2 years. A total of 230 children with primary headache (105 males, 125 females) were included. Two hundred two children were affected by migraine and 28 (12.2%) by other primary headaches. Cranial autonomic symptoms were significantly complained by migraineurs (55% vs 17.8%) (P < .001) and by children with higher frequency of migraine attacks (odds ratio = 2.6, confidence interval = 1.4-4.7, P = .001). Our findings show that cranial autonomic symptoms are rather common during pediatric migraine attacks. The association between cranial autonomic symptoms and higher frequency of attacks might suggest the role of the trigeminal-autonomic reflex in migraine pathophysiolog
New tools in percutaneous minimally invasive chronic subdural hematomas evacuation
Background: Incidence of chronic subdural hematomas (cSDH) is expected to progressive rise in the next decades. There is no univocal indication of the approach to be used. Furthermore, there is no data about the efficacy of twist drill craniostomy (TDC) in hematomas with membranes. Objective: To describe our modified technique for TDC in patients affected by cSDH with membranes and in treatment with antiplatelets. Methods: We analyzed a group of 37 patients, affected by cSDH with membrane (type D laminar membrane and type G trabecular membrane according to Nakaguchi classification), treated with mushroom TDC using a modified technique. Results: After surgery the average maximum thickness of the common postoperative liquoral subdural collection decreased from 18.8 to 6.21 mm. We documented one acute subdural hematoma (2.7%), asymptomatic and not treated, and one recurrence of cSDH (2.7%) after 2 months that needed re-intervention with single burr hole. Conclusions: We presented a modified twist drill technique, characterized by the introduction of an application of a new device that optimizes both surgical results, clinical outcome and surgical procedure time. The presence of membrane type D and G does not affect the efficacy of drainage, that is negatively related to the presence of clots or acute hematoma. This modified technique is safe, fast, effective and represents a valid first line treatment of an unstable and unpredictable pathology such as cSDH. We suggest performing such technique on a larger patientsâ cohort to further validate its effectiveness
ASTROPHYSICAL IMPACT of the UPDATED 9Be(p,)6Li and 10B(p,)7Be REACTION RATES AS DEDUCED by THM
The complete understanding of the stellar abundances of lithium, beryllium, and boron represents one of the most interesting open problems in astrophysics. These elements are largely used to probe stellar structure and mixing phenomena in different astrophysical scenarios, such as pre-main-sequence or main-sequence stars. Their different fragility against (p,) burning reactions allows one to investigate different depths of the stellar interior. Such fusion mechanisms are triggered at temperatures between T â (2-5) Ă K, thus defining a corresponding Gamow energy between â 3-10 keV, where S(E)-factor measurements need to be performed to get reliable reaction rate evaluations. The Trojan Horse Method is a well defined procedure to measure cross sections at Gamow energies overcoming the uncertainties due to low-energy S(E)-factor extrapolation as well as electron screening effects. Taking advantage of the measure of the 9Be(p,)6Li and 10B(p,)7Be cross sections, the corresponding reaction rates have been calculated and compared with the evaluations by the NACRE collaboration, widely used in the literature. The impact on surface abundances of the updated 9Be and 10B (p,) burning rates is discussed for pre-MS stars
Molecular Structures in T=1 states of 10B
Multi-center (molecular) structures can play an important role in light
nuclei. The highly deformed rotational band in 10Be with band head at 6.179 MeV
has been observed recently and suggested to have an exotic alpha:2n:alpha
configuration. A search for states with alpha:pn:alpha two-center molecular
configurations in 10B that are analogous to the states with alpha:2n:alpha
structure in 10Be has been performed. The T=1 isobaric analog states in 10B
were studied in the excitation energy range of E=8.7-12.1 MeV using the
reaction 1H(9Be,alpha)6Li*(T=1, 0+, 3.56 MeV). An R-matrix analysis was used to
extract parameters for the states observed in the (p,alpha) excitation
function. Five T=1 states in 10B have been identified. The known 2+ and 3-
states at 8.9 MeV have been observed and their partial widths have been
measured. The spin-parities and partial widths for three higher lying states
were determined. Our data support theoretical predictions that the 2+ state at
8.9 MeV (isobaric analog of the 7.54 MeV state in 10Be) is a highly clustered
state and can be identified as a member of the alpha:np:alpha rotational band.
The next member of this band, the 4+ state, has not been found. A very broad 0+
state at 11 MeV that corresponds to pure alpha+6Li(0+,T=1) configuration is
suggested and it might be related to similar structures found in 12C, 18O and
20Ne.Comment: 10 pages, 10 figures, accepted in Physical Review
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