Dynamical signatures of quantum chaos and relaxation time scales in a spin-boson system.

Quantum systems whose classical counterparts are chaotic typically have highly correlated eigenvalues and level statistics that coincide with those from ensembles of full random matrices. A dynamical manifestation of these correlations comes in the form of the so-called correlation hole, which is a dip below the saturation point of the survival probability's time evolution. In this work, we study the correlation hole in the spin-boson (Dicke) model, which presents a chaotic regime and can be realized in experiments with ultracold atoms and ion traps. We derive an analytical expression that describes the entire evolution of the survival probability and allows us to determine the time scales of its relaxation to equilibrium. This expression shows remarkable agreement with our numerical results. While the initial decay and the time to reach the minimum of the correlation hole depend on the initial state, the dynamics beyond the hole up to equilibration is universal. We find that the relaxation time of the survival probability for the Dicke model increases linearly with system size.

Helminth community from Azara's grass mouse (Akodon azarae) in three habitats with different land use in farming systems of Argentina.

In the Pampa region of Argentina, farming activities have been performed since the beginning of the 20th century, but in the 1990s, land-use patterns rapidly changed towards intensive agriculture and poultry breeding. This study compares the helminth community of Akodon azarae (Rodentia) among three habitats with different land use in pampean agroecosystems: poultry farms, mono-cultivated fields and abandoned fields (not used for 35 years), under the prediction that there will be greater helminth richness and diversity in mice from abandoned fields compared to those from the other habitats. Nevertheless, the highest abundance of A. azarae occurred on poultry farms, the habitat most disturbed by human activity, while cultivated fields showed the lowest. Helminth richness and diversity were significantly higher on poultry farms than in the other habitats, due to the presence of Trichuris laevitestis, Protospirura numidica criceticola and cysts of Taenia taeniaeformis. We suggest that the helminth fauna of A. azarae can survive on poultry farms despite disturbance from farming activities, because rodents can move and get shelter within farm perimeter fences, where dense and high vegetation grows. This farm area could offer good conditions for geohelminth development, while chicken sheds could attract insects that are intermediate hosts of helminths with indirect life cycles. On the contrary, agrochemicals applied in cultivated fields would negatively influence helminth diversity and composition, by decreasing host populations (arthropods and rodents) and affecting free larval stages of geohelminths.

Dynamical manifestations of quantum chaos: correlation hole and bulge.

A main feature of a chaotic quantum system is a rigid spectrum where the levels do not cross. We discuss how the presence of level repulsion in lattice many-body quantum systems can be detected from the analysis of their time evolution instead of their energy spectra. This approach is advantageous to experiments that deal with dynamics, but have limited or no direct access to spectroscopy. Dynamical manifestations of avoided crossings occur at long times. They correspond to a drop, referred to as correlation hole, below the asymptotic value of the survival probability and to a bulge above the saturation point of the von Neumann entanglement entropy and the Shannon information entropy. By contrast, the evolution of these quantities at shorter times reflects the level of delocalization of the initial state, but not necessarily a rigid spectrum. The correlation hole is a general indicator of the integrable-chaos transition in disordered and clean models and as such can be used to detect the transition to the many-body localized phase in disordered interacting systems.This article is part of the themed issue 'Breakdown of ergodicity in quantum systems: from solids to synthetic matter'.

Estudio comparativo de cierre de cuero cabelludo en neurocirugías supratentoriales: intradérmica vs. surget / Comparative study of scalp closure in supratentorial neurosurgery: intradermal vs. surget

Introducción: El cierre de cuero cabelludo en neurocirugías supratentoriales mediante sutura intradérmica es una técnica poco difundida en la actualidad. En contraste, es común que se efectúen suturas de alta tensión con el fin de evitar dehiscencias, fístula de líquido cefalorraquídeo (LCR) y sangrado durante el período posquirúrgico, pero que no tienen buen resultado estético. Objetivo: Comparar las complicaciones relacionadas al cierre de cuero cabelludo que se presentaron en neurocirugías supratentoriales en un período de 19 meses, para determinar si utilizar un cierre de menor tensión y con mejor resultado estético, es igual de seguro que las técnicas de cierre habituales. Materiales y Métodos: Se incluyeron 84 casos de neurocirugías supratentoriales electivas. En 43 casos (control) se realizó el cierre mediante sutura continua tipo surget y en 41 casos (experimental) el cierre fue mediante sutura intradérmica. Resultados: Se presentaron 2 casos de infecciones, 1 en cada grupo (p= 0,97) y 1 caso de sangrado en el grupo control (p= 0,32). No se presentaron dehiscencias ni casos de fístula de LCR. Conclusiones: El cierre de cuero cabelludo mediante sutura intradérmica fue un método seguro que no generó una mayor incidencia de complicaciones y logró un mejor resultado estético a corto y largo plazo.

Background: Scalp closure by means of intradermal suture in patients who underwent supratentorial neurosurgeries is currently an uncommon technique. In contrast, it is usual to perform high tension sutures to avoid skin dehiscence, cerebrospinal fluid leak (CSF) and postoperative bleeding; however it usually results in unsatisfactory aesthetic results. Aim: Comparing complications, over a two year period, related to scalp closure occurred in supratentorial neurosurgeries. The goal is to establish if the intradermal suture is as safe as the current high tension closure technique.Materials and Methods: Eighty-four patients were included. In forty-three cases (control) continuous high tension suture (surget) was performed. The other forty-one cases (experimental) underwent intradermal suture. Results: Two infection cases occurred, one from each group (p= 0, 97). There was one case of bleeding that took place in the control group (p= 0,32). Neither dehiscence nor CSF leak occurred in any of the trial cases.Conclusions: Intradermal suture performed for scalp closure was as safe as surget in terms of complications occurrence and obtained better cosmetic results in the short and long term.

Nuestra experiencia en el manejo de los cavernomas de tronco, de tálamo y de ganglios basales / Our experience in the management of trunk, thalamus and basal ganglia cavernomas

OBJETIVO: Presentar nuestra experiencia en el manejo de los cavernomas de tronco cerebral, de tálamo y de ganglios basales. MATERIAL Y MÉTODO: Analizamos una serie de 16 pacientes asistidos en nuestra Institución, entre enero de 1990 y diciembre del año 2013. De ellos, 9 fueron varones y 7 mujeres. El rango de edad osciló entre 3 y 61 años. RESULTADOS: Siete debutaron con hemorragia cerebral, de ellos 4 se localizaban en protuberancia y 3 en el bulbo raquídeo. Siete pacientes tuvieron cavernomas múltiples, de ellos 3 tenían familiares con la misma enfermedad. El procedimiento diagnóstico de elección fue la resonancia nuclear magnética de cerebro en todos, y en los pacientes con cavernomas múltiples se completó el estudio con resonancia nuclear magnética de médula espinal. El tratamiento fue conservador en 9 enfermos, quirúrgico en 6 y radiocirugía estereotáctica en 1 enfermo; a éste paciente hubo necesidad de operarlo 6 meses después del tratamiento radiante por un resangrado voluminoso en la protuberancia. DISCUSIÓN: La cirugía es exitosa cuando el cavernoma se ubica a 2 mm de la piamadre, o del epéndimo. La radiocirugía puede ser causante de resangrado y de mayor volumen que las hemorragias previas. Por último, el tratamiento conservador sigue teniendo vigencia en los pacientes que se recuperaron neurológicamente y cuando se ubican en la profundidad del tronco cerebral, tálamo óptico o ganglios basales. CONCLUSIÓN: Cada paciente debe evaluarse individualmente para decidir el tipo de tratamiento, teniendo en cuenta la edad, la recuperación de los signos neurológicos, el volumen y la localización precisa del cavernoma

Objective: To present our experience in the management of brainstem, thalamus and basal ganglia cavernous malformations. Material and Method: We analyzed a series of 16 patients admitted to our Institution between January 1990 and December 2013. Nine of them were male and 7 female. Age ranged between 3 and 61. Results: Seven patients presented brainstem hemorrhage, 4 being pontine and the remaining 3 were medullary. Seven patients had multiple cavernomas, and 3 of them had a family background with the disease. The chosen diagnostic procedure was brain MRI in all patients; in patients with multiple cavernomas spine MRI was also requested. Nine patients received conservative treatment, 6 patients underwent surgery and one was treated with stereotactic radiosurgery but had to be operated on six months after radiation treatment due to voluminous re-bleeding at protuberance. Discussion: Surgery is successful when the cavernous malformation is placed 2 mm away from pia mater or ependyma. Radiosurgery can cause re-bleeding and of a greater volume than previous hemorrhages. Finally, conservative treatment is useful in patients who get neurologically recovered and when malformations are placed deep in brainstem, optic thalamus or basal ganglia. Conclusion: Each patient has to be individually assessed to individually assessed to make a decision regarding the type of treatment, taking into account age, recovery of neurological signs, volume, and precise location of cavernous malformation

Local quenches with global effects in interacting quantum systems.

We study one-dimensional lattices of interacting spins-1/2 and show that the effects of quenching the amplitude of a local magnetic field applied to a single site of the lattice can be comparable to the effects of a global perturbation applied instantaneously to the entire system. Both quenches take the system to the chaotic domain, the energy distribution of the initial states approaches a Breit-Wigner shape, the fidelity (Loschmidt echo) decays exponentially, and thermalization becomes viable.

Effects of the interplay between initial state and Hamiltonian on the thermalization of isolated quantum many-body systems.

We explore the role of the initial state on the onset of thermalization in isolated quantum many-body systems after a quench. The initial state is an eigenstate of an initial Hamiltonian H(I) and it evolves according to a different final Hamiltonian H(F). If the initial state has a chaotic structure with respect to H(F), i.e., if it fills the energy shell ergodically, thermalization is certain to occur. This happens when H(I) is a full random matrix, because its states projected onto H(F), are fully delocalized. The results for the observables then agree with those obtained with thermal states at infinite temperature. However, finite real systems with few-body interactions, as the ones considered here, are deprived of fully extended eigenstates, even when described by a nonintegrable Hamiltonian. We examine how the initial state delocalizes as it gets closer to the middle of the spectrum of H(F), causing the observables to approach thermal averages, be the models integrable or chaotic. Our numerical studies are based on initial states with energies that cover the entire lower half of the spectrum of one-dimensional Heisenberg spin-1/2 systems.

Time fluctuations in isolated quantum systems of interacting particles.

Numerically, we study the time fluctuations of few-body observables after relaxation in isolated dynamical quantum systems of interacting particles. Our results suggest that they decay exponentially with system size in both regimes, integrable and chaotic. The integrable systems considered are solvable with the Bethe ansatz and have a highly nondegenerate spectrum. This is in contrast with integrable Hamiltonians mappable to noninteracting ones. We show that the coefficient of the exponential decay depends on the level of delocalization of the initial state with respect to the energy shell.

Diversity of the helminth community of the Pampean grassland mouse (Akodon azarae) on poultry farms in central Argentina.

This paper describes the helminth community of the Pampean grassland mouse (Akodon azarae) inhabiting poultry farms in central Argentina. Winter diversity (season of high rodent abundance) has been compared to spring diversity (season of low rodent abundance). Species richness was seven in both seasons: five nematodes (Syphacia carlitosi, Stilestrongylus spp., Trichuris laevitestis, Pterygodermatites (Paucipectines) azarai and Protospirura numidica criceticola) and two cestodes (adults of Cyclophyllidea and Taenia taeniaeformis hepatic cysts). No difference in richness was detected between host sexes in each season or among host age classes. However, the helminth community showed 67% similarity between winter and spring, with diversity being significantly higher in spring (H = 0.873) than in winter (H = 0.546; P < 0.0005). This could be attributed to different factors, such as host abundance, host diet or environmental factors, that affect the transmission of each species differently. On the other hand, Stilestrongylus spp. and S. carlitosi showed higher dominance and intensity in both seasons compared to their cohabiting species, P. (P.) azarai and T. laevitestis, respectively. The lower values of the latter two species may be related to a crowding effect due to their large body sizes. This is the first report of cestodes in A. azarae. The finding of T. taeniaeformis strobilocerci could be important in the epidemiology of parasitosis in domestic animals of the farms.

Interstitial stereotactic radiosurgery of pilocytic astrocytomas in paediatric patients.

OBJECTIVE: To evaluate the clinical presentation, tumour response, clinical improvement and complications in 12 children and young people with a pilocytic astrocytoma, WHO I grade 1, who were treated with interstitial radiosurgery using Iodine-125 seed implants. PATIENTS AND METHODS: Retrospective analysis of 12 patients aged under 18 years (mean 8.4 years, ranging from 8 months to 17 years of age) with a pilocytic astrocytoma treated between 1993 and 2006. Iodine-125 seeds were used as temporary implants with low-dose rate (

Management of child optic pathway gliomas: new therapeutical option.

OBJECTIVE: To present our experience in the treatment of child optic pathway gliomas in the last 25 years. MATERIAL AND METHODS: Seventeen children under 10 years of age have been analyzed and assessed from clinic, ophthalmologic, endocrinologic, neurological, neuropathologic, and imaginologic points of view. RESULTS: Predominance of female patients, 10 girls and 7 boys between 6 and 122 months old; mean age was 3 years and 8 months. The most frequent symptoms have been ophthalmologic and visual alterations in all 17 patients, endocrine alterations in 10, and neurological signs in 6. One of the patients presented neurofibromatosis type 1 (NF1), another patient had Down syndrome. Diagnosed using computed tomography or/and magnetic resonance imaging, histological studies showed pilocytic astrocytomas in 13 cases and a fibrillary astrocytoma grade II in 1 case. There were three patients without histological diagnosis; one of them had NF1. The treatment consisted of surgery, external beam radiotherapy, chemotherapy, and brachytherapy with iodine 125, separately or combined. Five patients died; the causes were secondary tumors in two children, tumor recurrence in one, sepsis secondary to respiratory and urinary tract infections in the child with Down syndrome, and finally, hydrocephaly due to hyperproteinorachia of tumor origin in one. Average survival was 89 months. CONCLUSION: Chemotherapy and brachytherapy are therapeutic methods to be considered, especially in children under 5. Marsupialization of the residual cyst into the ventricular system postradio or oncolytic treatment through endoscopic or stereotactic techniques is useful in the treatment of endocranial hypertension and/or hypothalamic compression in these patients.

Cerebellar astrocytomas: a 24-year experience.

INTRODUCTION: Cerebellar astrocytomas are the most benign tumors of the CNS. Seventy to eighty percent are found in children. METHODS AND RESULTS: We report on 38 children under 18 who had cerebellar astrocytoma in the posterior fossa and were treated by a multidisciplinary team in our Neurosurgical Department from January 1974 to December 1997. We included all patients in whom the histopathological diagnosis was astrocytoma, regardless of malignancy. The diagnostic methods used were pneumoventriculography, cranial X-rays, CT scan, and MRI. All patients were treated surgically. Neither radiotherapy nor chemotherapy was indicated in patients with pilocytic or fibrillary astrocytomas. A greater prevalence was observed in female (25/38; 66%) than in male (13/38; 34%) patients. Histopathological results revealed 27 (71%) pilocytic astrocytomas, 8 (21%) diffuse fibrillary astrocytomas, 1 (2%) anaplastic astrocytoma and 2 (6%) glioblastomas. These tumors were more frequently located in the right cerebellar hemisphere; increased intracranial pressure syndrome was the most frequent form of clinical presentation. Total tumor resection was obtained in 29 (83%) cases and subtotal resection in 9 (17%). In 6 (16%) cases, ventriculoperitoneal shunts were placed to control persistent hydrocephalus after tumor excision. CONCLUSION: The most frequent complication was increased ataxia. The mortality rate was 8.5%.

Nuestra experiencia en el manejo de los angiomas cavernosos del sistema nervioso central / Our experience in the management of cavernomas

El objetivo del presente trabajo es analizar nuestra experiencia en el manejo de los cavernomas del sistema nervioso central (SNC). Se analizaron, retrospectivamente, aspectos epidemiológicos, clínicos, diagnósticos y terapéuticos de 22 pacientes admitidos al Servicio de Neurocirugía del Sanatorio Allende entre enero de 1985 y diciembre de 1999 con diagnóstico de cavernoma del SNC. La muestra está compuesta por nueve pacientes menores de 15 años y 13 adultos, 13 varones y 9 mujeres. Se incluyen 3 pacientes de sexo masculino familiares directos (cavernomatosis familiar). Doce pacientes consultaron por convulsiones (3 de ellos con epilepsia refractaria), ocho por déficit neurológico, uno por cefalea y otro asintomático miembro de la familia portadora de cavernomas múltiples. En todos los casos el diagnóstico se realizó con RNM. De 18 pacientes a los que se les realizó TAC, en seis casos el estudio reveló anomalias, en cinco se observaron calcificaciones, en otros cinco se observaron signos de sangrado agudo y en uno se demostró una lesión hipodensa en el sitio donde posteriormente se confirmó el cavernoma. En cuanto a la localización 13 casos fueron supratentoriales (5 temporales, 4 parietales, 2 frontales, 1 occipital y 1 de ganglios basales) y 2 medulares cervicales. Doce pacientes fueron operados, 7 por convulsiones (3 con epilepsia refractaria) y los cinco restantes por déficit neurológico; 6 recibieron sólo drogas antiepilépticas y en 4 casos la observación fue la única medida. En el postoperatorio inmediato un paciente falleció por hematomas cerebrales múltiples diagnosticándose histopatológicamente amiloidosis cerebral primaria, uno presentó hipo incoercible, uno hemianopsia homónima y otro presentó una fístula del LCR tratada médicamente. Los pacientes con epilepsia refractaria lograron controlar las crisis y uno se encuentra actualmente sin medicación alguna. La media de seguimiento clínico fue de 72 meses y el rango 1 a 180 meses

Postraumatic intracranial hematomas in infancy. a 16-year experience.

OBJECTS: The objective of this study is to analyze some of the epidemiological aspects in patients with post-traumatic intracranial hematomas (post-traumatic ICH) in infancy. These patients were treated at the Hospital Infantil Municipal de Córdoba, Argentina, between April 1980 and April 1996. METHODS: A retrospective descriptive analysis was conducted on the 113 case histories of children with post-traumatic ICH, all of whom required surgical intervention during this period. Relevant information such as age, sex, mechanism of injury causing craniocerebral trauma (CCT), and data on clinical presentation on admission, diagnosis, morbidity and mortality rates were collected. CONCLUSIONS: The series revealed a greater incidence of post-traumatic ICH in boys (73.5%), whose average age was 6 years 5 months +/- 4 years 10 months (range 1 day to 15 years). Fifty-three percent of the girls suffered post-traumatic ICH before the age of 3, while 54% of the children were 7 years of age or older (P<0.05). Falls were the most frequent mechanism of injury causing CCT (36.3%), followed by vehicle accidents (33.6%) and unknown causes (15.9%), the latter mainly in children under 3 years old (31%). The most frequent symptoms were vomiting (58.6%), loss of consciousness (47.1%) and headaches (24.1%). Of all these children, 93.8% presented signs and symptoms at the time of hospital admission, alterations in the level of consciousness (66%), vomiting (47.2%) and headaches (26.4%) being among the most frequent. The hemorrhagic complications observed in the 113 patients took the form of extradural hematomas (EDH) in 75 (66.4%), of subdural hematomas (SDH) in 35 (31.0%), of hemorrhagic contusions (Hc) in 19 (16.8%), and of intracerebral hematomas (Ich) in 11 (9.7%). In 13 patients the site of the hematoma was the posterior cranial fossa (11.5%), and 22.1% of patients presented more than one type of hemorrhagic complication. Morbidity rates were 9.7% and mortality rates 17.7%.

Posteroventral pallidotomy in Parkinson's disease.

OBJECTIVE: We analyse the clinical aspects, results and reliability of posteroventral pallidotomy (PVP) carried out as treatment for the principal symptoms and treatment induced complications in patients with Parkinson's disease (PD). PATIENTS AND METHODS: Between August 1995 January 1998, 17 patients with PD were treated surgically, 13 patients with PVP. A pre- and post-surgical clinical evaluation was carried out. Riechert's Stereotactic System (MHT, Freiburg, Germany) was used. Ventriculography under stereotactic conditions was used in the PVP procedures, Laitinen's co-ordinates as anatomical target, and electrical stimulation for physiological determination. 3 4 radiofrequency lesions were made at 83 degrees C for 20". The mean age was 60 +/- 10.8 years, ages ranging from 45-79 years. 8 (60.5%) of the patients were male. The cardinal symptoms of the series were bradykinesia and rigidity. The duration of the illness ranged from 8.6 +/- 3.7 years with a range of 4-15 years. 7 (53.8%) presented with a duration of 10 years or more. 6 (46,2%) of the patients underwent left PVP, the remaining 7 (53.8%) right PVP. Only one patient received treatment with right PVP and ipsilateral thalamotomy in the same surgical procedure. The mean post-surgical follow up was 16 +/- 7 months, with a range of 2 to 26 months. RESULTS: An up to date evaluation was carried out on all patients showing significant changes after PVP in UPDRS motor (P < 0.005), complete rigidity relief (P < 0.005), bradykinesia relief (P < 0.005) and complete tremor relief (P < 0.005). An important improvement in contralateral dyskinesia was noted after PVP. A subjective evaluation of the results showed excellent results in 4 (30.8%) patients, good in 6 (46.2%) and fair in 3 (23%). No significant correlation was found between age and duration of illness (P = 0.7). Two patients suffered slight side effects, one patient with worsening of hypophonia whilst the other suffered subjective visual impairment controlled by normal post operative ophthalmological examinations. There was no peri-operative mortality. CONCLUSION: PVP is considered a safe and effective surgical method for the treatment of both the principal symptoms of PD and the complications of DOPA medication.

Stereotactic neurosurgery in children and adolescents.

Between March 1992 and January 1998, 100 stereotactic procedures were carried out in our Stereotactic Department. Of these, 24 were performed on patients under 18 years of age, 22 of them under a local anaesthetic and sedation. The ages of these patients ranged between 4 months and 18 years. The stereotactic procedures carried out were: 15 cerebral biopsies, 5 iodine-125 implants, 4 implantations of Rickham reservoirs with ventricular catheter, with additional holes to establish a connection between the cyst content and the ventricular system (internal drainage): 2 of these patients had arachnoidal cysts in the pineal region, 1 a thalamic neuroepithelial cyst and 1 a cystic craniopharyngioma, with excellent control of hydrocephalus. All cerebral biopsies were positive, including 3 in which brain stem tumours were detected. Of the 5 patients treated by brachytherapy, 4 had pilocytic astrocytomas and 1 an anaplastic astrocytoma. The sites of the tumours for which implants were used were the thalamus in 4 cases, and the basal ganglia (corpus striatum) in 1. In only 2 cases was there some transistory morbidity, and mortality was nil. The stereotactic procedures in this varied group were well tolerated, with low morbidity and mortality rates, which proves that this method is effective and safe for patients. It can also be used for the diagnosis of brain stem tumours. Midline cysts can also be treated by means of internal drainage with catheters (a minimally invasive form of surgery).