Neel Order and Electron Spectral Functions in the Two-Dimensional Hubbard Model: a Spin-Charge Rotating Frame Approach

Using recently developed quantum SU(2)xU(1) rotor approach, that provides a self-consistent treatment of the antiferromagnetic state we have performed electronic spectral function calculations for the Hubbard model on the square lattice. The collective variables for charge and spin are isolated in the form of the space-time fluctuating U(1) phase field and rotating spin quantization axis governed by the SU(2) symmetry, respectively. As a result interacting electrons appear as composite objects consisting of bare fermions with attached U(1) and SU(2) gauge fields. This allows us to write the fermion Green's function in the space-time domain as the product CP^1 propagator resulting from the SU(2) gauge fields, U(1) phase propagator and the pseudo-fermion correlation function. As a result the problem of calculating the spectral line shapes now becomes one of performing the convolution of spin, charge and pseudo-fermion Green's functions. The collective spin and charge fluctuations are governed by the effective actions that are derived from the Hubbard model for any value of the Coulomb interaction. The emergence of a sharp peak in the electron spectral function in the antiferromagnetic state indicates the decay of the electron into separate spin and charge carrying particle excitations.Comment: 16 pages, 5 figures, submitted to Phys. Rev.

LA PRESBYACOUSIE (PRISE EN CHARGE MEDICALE EN INSTITUTION)

PARIS6-Bibl.Pitié-Salpêtrie (751132101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

The role of cervical and ocular vestibular evoked myogenic potentials in the assessment of patients with vestibular schwannomas.

OBJECTIVES: To investigate the clinical utility of VEMPs in patients suffering from unilateral vestibular schwannoma (VS) and to determine the optimal stimulation parameter (air conducted sound, bone conducted vibration) for evaluating the function of the vestibular nerve. METHODS: Data were obtained in 63 patients with non-operated VS, and 20 patients operated on VS. Vestibular function was assessed by caloric, cervical and ocular VEMP testing. 37/63 patients with conclusive ACS ocular VEMPs responses were studied separately. RESULTS: In the 63 non-operated VS patients, cVEMPs were abnormal in 65.1% of patients in response to AC STB and in 49.2% of patients to AC clicks. In the 37/63 patients with positive responses from the unaffected side, oVEMPs were abnormal in 75.7% of patients with ACS, in 67.6% with AFz and in 56.8% with mastoid BCV stimulation. In 16% of the patients, VEMPs were the only abnormal test (normal caloric and normal hearing). Among the 26 patients who did not show oVEMP responses on either side with ACS, oVEMPs responses could be obtained with AFz (50%) and with mastoid stimulation (89%). CONCLUSIONS: The VEMP test demonstrated significant clinical value as it yielded the only abnormal test results in some patients suffering from a unilateral vestibular schwannoma. For oVEMPs, we suggest that ACS stimulation should be the initial test. In patients who responded to ACS and who had normal responses, BCV was not required. In patients with abnormal responses on the affected side using ACS, BCV at AFz should be used to confirm abnormal function of the superior vestibular nerve. In patients who exhibited no responses on either side to ACS, BCV was the only approach allowing assessment of the function of the superior vestibular nerve. We favor using AFz stimulation first because it is easier to perform in clinical practice than mastoid stimulation

A New Sensitive Test Using Virtual Reality and Foam to Probe Postural Control in Vestibular Patients: The Unilateral Schwannoma Model

International audienceVestibular schwannomas (VS) are benign tumors of the vestibular nerve that may trigger hearing loss, tinnitus, rotatory vertigo, and dizziness in patients. Vestibular and auditory tests can determine the precise degree of impairment of the auditory nerve, and superior and inferior vestibular nerves. However, balance is often poorly quantified in patients with untreated vestibular schwannoma, for whom validated standardized assessments of balance are often lacking. Balance can be quantified with the EquiTest. However, this device was developed a long time ago and is expensive, specific, and not sensitive enough to detect early deficits because it assesses balance principally in the sagittal plane on a firm platform. In this study, we assessed postural performances in a well-defined group of VS patients. We used the Dizziness Handicap Inventory (DHI) and a customized device consisting of a smartphone, a mask delivering a fixed or moving visual scene, and foam rubber. Patients were tested in four successive sessions of 25 s each: eyes open (EO), eyes closed (EC), fixed visual scene (VR0), and visual moving scenes (VR1) delivered by the HTC VIVE mask. Postural oscillations were quantified with sensors from an android smartphone (Galaxy S9) fixed to the back. The results obtained were compared to those obtained with the EquiTest. Vestibulo-ocular deficits were also quantified with the caloric test and vHIT. The function of the utricle and saccule were assessed with ocular and cervical vestibular-evoked myogenic potentials (o-VEMPs and c-VEMPs), respectively. We found that falls and abnormal postural oscillations were frequently detected in the VS patients with the VR/Foam device. We detected no correlation between falls or abnormal postural movements and horizontal canal deficit or age. In conclusion, this new method provides a simpler, quicker, and cheaper method for quantifying balance. It will be very helpful for (1) determining balance deficits in VS patients; (2) optimizing the optimal therapy indications (active follow-up, surgery, or gamma therapy) and follow-up of VS patients before and after treatment; (3) developing new rehabilitation methods based on balance training in extreme conditions with disturbed visual and proprioceptive inputs

Early functional results using the nitibond prosthesis in stapes surgery

Conclusion:The NiTiBONDVRprosthesis allows early results to be obtained similar to those with amanually crimped prosthesis fitted by experienced surgeons, thus reducing the learning curve in thiscritical step of the procedure.Objective:To analyze the 1-month results using the nitinol NiTiBONDVRprosthesis in primaryotosclerosis surgery and to compare the results with those obtained with fully fluoroplastic or fullytitanium pistons.Materials and methods:Fifty consecutive cases operated on with the NiTiBONDVRprosthesis (nitinolgroup) were compared with 50 cases operated on with a fully fluoroplastic piston (fluoroplastic group),and with 131 cases operated on with a fully titanium piston (first titanium group), and also with50 cases operated on with the same titanium piston just before using the NiTiBONDVRpiston (last titan-ium group). Pure-tone and speech audiometry was performed 1 month after surgery for the nitinolgroup. Comparison was made between the early hearing results of the four groups.Results:The mean air–bone gap closure for the nitinol group was 16± 1.0dB (mean ± SEM,n¼50); anair–bone gap of<15 dB and<10 dB was obtained in 100% and 84% of cases, respectively. These hear-ing results were similar to the last titanium group and significantly better than those observed in thefluoroplastic and first titanium groups

Means (±SD) peak-to-peak amplitude of cVEMPs induced by AC STB and clicks, and mean (±SD) peak-to-peak amplitude of oVEMPs induced by AC STB and BCV (AFz and mastoid), in healthy subjects, 63 patients with non-operated VS (affected and intact side) and 20 patients after surgery for VS (intact side).

<p>*Significantly different to healthy subjects (<i>t</i>-test).</p><p>VS: vestibular schwanomma.</p><p>VEMPs: vestibular evoked myogenic potentials.</p><p>cVEMPs: cervical VEMPs.</p><p>oVEMPs: ocular VEMPs.</p><p>AC: air-conducted.</p><p>BCV: bone-conducted vibration.</p><p>STB: short-tone bursts.</p

Results for six VS patients with abnormal cervical and/or ocular VEMPs but normal caloric and hearing tests.

<p>Patient 5 is illustrated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0105026#pone-0105026-g002" target="_blank">figure 2</a>.</p><p>CPA: cerebello-pontine angle.</p><p>IC: intracanalar.</p><p>The response was defined as normal if the EPr was below the threshold value and abnormal (abolished or decreased) if EPr was above the threshold.</p

Flowchart showing the oVEMP results for non-operated VS patients (n = 63).

<p>Results are presented according to the following test sequence: AC STB, AFz BCV and mastoid BCV. This sequence is optimal to provide reliable conclusions about the functional status of the inferior (mostly utricular) nerve in a minimum of time. Patients with normal ACS oVEMPs always exhibited normal AFz and normal mastoid oVEMPs (Figure 3, grey squares). Patients with abnormal oVEMPs also exhibited abnormal AFz (25 of 28 patients) and abnormal mastoid oVEMPs (21 of 28 patients) (Figure 3, purple squares). Abnormal ACS but normal BCV oVEMPs were observed in three of 28 patients for AFz and in seven of 28 patients for mastoid BCV (Figure 3, yellow squares). Among the 26 ACS NR patients, 13 were NR for AFz BCV and three were NR for mastoid BCV(green squares).</p

Number (%) of operated VS patients (n = 20) with abnormal responses or no responses on either side to VEMP tests.

<p>Note that for the mastoid BCV stimulation, three patients were not included because of the consequences of the surgery on the mastoid process.</p