High-Frequency Sound in a Unitary Fermi Gas.

We present an experimental and theoretical study of the phonon mode in a unitary Fermi gas. Using two-photon Bragg spectroscopy, we measure excitation spectra at a momentum of approximately half the Fermi momentum, both above and below the superfluid critical temperature T_{c}. Below T_{c}, the dominant excitation is the Bogoliubov-Anderson (BA) phonon mode, driven by gradients in the phase of the superfluid order parameter. The temperature dependence of the BA phonon is consistent with a theoretical model based on the quasiparticle random phase approximation in which the dominant damping mechanism is via collisions with thermally excited quasiparticles. As the temperature is increased above T_{c}, the phonon evolves into a strongly damped collisional mode, accompanied by an abrupt increase in spectral width. Our study reveals strong similarities between sound propagation in the unitary Fermi gas and bosonic liquid helium.

Energy and contact of the one-dimensional Fermi polaron at zero and finite temperature.

We use the T-matrix approach for studying highly polarized homogeneous Fermi gases in one dimension with repulsive or attractive contact interactions. Using this approach, we compute ground state energies and values for the contact parameter that show excellent agreement with exact and other numerical methods at zero temperature, even in the strongly interacting regime. Furthermore, we derive an exact expression for the value of the contact parameter in one dimension at zero temperature. The model is then extended and used for studying the temperature dependence of ground state energies and the contact parameter.

Exotic superfluid states of lattice fermions in elongated traps.

We present real-space dynamical mean-field theory calculations for attractively interacting fermions in three-dimensional lattices with elongated traps. The critical polarization is found to be 0.8, regardless of the trap elongation. Below the critical polarization, we find unconventional superfluid structures where the polarized superfluid and Fulde-Ferrell-Larkin-Ovchinnikov-type states emerge across the entire core region.

Induced interactions and the superfluid transition temperature in a three-component Fermi gas.

We study many-body contributions to the effective interaction between fermions in a three-component Fermi mixture. We find that effective interactions induced by the third component can lead to a phase diagram different from that predicted if interactions with the third component are neglected. As a result, in a confining potential a superfluid shell structure can arise even for equal populations of the components. We also find a critical temperature for the BCS transition in a 6Li mixture which can deviate strongly from the one in a weakly interacting two-component system.

Perfusion CT of the brain in the assessment of flow alterations during brachytherapy of meningioma.

PURPOSE: The aim was to investigate the use of perfusion CT of the brain in the assessment of flow alterations during brachytherapy of meningiomas. MATERIAL AND METHODS: Six patients with an intracranial meningioma were investigated during brachytherapy treatment by stereotactic implantation of I-125 seeds. Cerebral blood flow (CBF) in the tumour centre and the tumour periphery as well as in the normal brain parenchyma was determined by perfusion CT. Follow-up examinations were performed during the first year after the implantation. The CBF of the normal brain parenchyma was used as control. RESULTS: In the beginning of therapy, the mean+/-SEM blood flow in the tumour centre was 231.4+/-58.1 ml/100 g/min and in the periphery 223.5+/-53.8 ml/100 g/min. Within three months after the iodine seed implantation, the tumour blood flow had decreased 41%. At the one-year follow-up, the tumour blood flow in the centre had decreased to 68.7+/-45.9 ml/100 g/min. In the periphery of the tumour, it remained nearly unchanged (199.3+/-101.0 ml/100 g/min). The CBF values obtained from normal brain parenchyma did not decrease during the treatment. Throughout the study, the mean CBF for the normal grey matter was 38.5+/-2.9 ml/100 g/min, and 22.3+/-1.2 ml/100 g/min for the normal white matter. CONCLUSION: Perfusion CT seems to enable accurate monitoring of the blood flow of meningiomas during brachytherapy, and could be used in clinical situations where blood flow changes in brain and tumours should be investigated.

Multiple schwannomas: schwannomatosis or neurofibromatosis type 2?

OBJECT: The aim of this study was to clarify the clinical outcome of schwannomatosis, a rare condition characterized by multiple nonvestibular schwannomas in the absence of meningiomas, intraspinal ependymomas, and other clinical signs of neurofibromatosis type 2 (NF2). METHODS: Nine patients with schwannomatosis treated at one institution are presented and their clinical course during a median follow-up time of 9.9 years is discussed. The patients were typically middle-aged at the time of their first operation (median 43.5 years), none had a positive family history of schwannomatosis or NF2, and none showed cutaneous or ocular signs of NF2. On histopathological examination the tumors from the patients with schwannomatosis showed a lobular appearance and frequent Verocay bodies, signs indicating NF2, more often than 20 sporadic schwannomas that were investigated as controls. Two patients died of unrelated causes at 3.2 and 9.9 years, respectively, of follow up. Magnetic resonance images of the head and spine were obtained in seven patients at the end of the follow-up period. New spinal schwannomas were detected in one patient and a residual schwannoma in three. No germline mutations of the NF2 gene were found in these seven patients. Two additional patients originally included in the schwannomatosis group who were 8.6 and 11.7 years old at initial surgery had NF2. One was diagnosed at follow-up review and the other developed a fulminant disease that led to death in 4 years. CONCLUSIONS: The clinical course, long-term outcome, and genetic mechanism of schwannomatosis differ from that of NF2.