Fast positronium formation and dissociation at surfaces

The origin of short‐lived components in the annihilation lifetime spectrum of positronium (Ps) is shown to be due to fast Ps that is collisionally dissociating at the surfaces of the surrounding confinement cavity. The results are consistent with a model of fast (10–100 eV) Ps production by backscattered positrons from the incident beam. It is found that the typical lifetime of dissociating Ps scales with the mean free path of the cavity, and the relative formation intensity depends inversely on the incident positron beam energy. This ubiquitous effect will be present in any Ps formation experiment involving a free surface and can only be eliminated at beam energies less than 10 eV. More practical methods of minimizing the undesirable systematic effects of fast Ps quenching in depth‐profiled positron lifetime spectroscopy and in precision Ps decay rate measurements will be discussed. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70565/2/JAPIAU-78-3-1406-1.pd

Measurement of the vacuum decay rate of orthopositronium formed in an MgO-lined cavity

Orthopositronium decay rates are measured in MgO-lined cavities with various volumes and entrance apertures. Systematic effects of the entrance aperture, cavity geometry, and collisional pick-off are measured. The vacuum decay rate is determined to be 7.050 +/- 0.013 [mu]s-1.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22484/1/0000025.pd

The decay rate of orthopositronium

We review recent measurements of the orthopositronium decay rate, λT, and present results of a new 230‐ppm measurement using the vacuum technique. It corroborates, at the 6.2 sigma level, the discrepancy between theory and a recent 200‐ppm measurement of λT in gases.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87568/2/481_1.pd

A viable superluminal hypothesis: Tachyon emission from orthopositronium

Tachyons are hypothetical particles that travel faster than the vacuum speed of light. Previous experiments have searched for, but have not found evidence of tachyons. Long-standing, anomalous measurements of the orthopositronium (o-Ps) decay rate are interpreted as evidence for two tachyons being occasionally emitted when o-Ps decays. Restricting the coupling of tachyon pairs to a single photon (no tachyon coupling to matter) yields a new theory where tachyons are only observed in o-Ps decay and not in the previous tachyon experiments. Combining the single photon coupling theory with all previous experiments predicts that these tachyons must deposit energy while traversing scintillator detectors. A new tachyon search experiment will use this energy loss prediction to attempt to find tachyons passing through the apparatus or set limits disproving the original o-Ps to tachyon hypothesis. Viewing an intense o-Ps source, a time-of-flight spectrometer uses the superluminal property of tachyons for identification. Several months of continuous data acquisition will be necessary to completely eliminate the o-Ps to tachyon hypothesis. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87640/2/1119_1.pd

Low early ototoxicity rates for pediatric medulloblastoma patients treated with proton radiotherapy

<p>Abstract</p> <p>Background</p> <p>Hearing loss is common following chemoradiotherapy for children with medulloblastoma. Compared to photons, proton radiotherapy reduces radiation dose to the cochlea for these patients. Here we examine whether this dosimetric advantage leads to a clinical benefit in audiometric outcomes.</p> <p>Methods</p> <p>From 2006-2009, 23 children treated with proton radiotherapy for medulloblastoma were enrolled on a prospective observational study, through which they underwent pre- and 1 year post-radiotherapy pure-tone audiometric testing. Ears with moderate to severe hearing loss prior to therapy were censored, leaving 35 ears in 19 patients available for analysis.</p> <p>Results</p> <p>The predicted mean cochlear radiation dose was 30 ⁶⁰Co-Gy Equivalents (range 19-43), and the mean cumulative cisplatin dose was 303 mg/m²(range 298-330). Hearing sensitivity significantly declined following radiotherapy across all frequencies analyzed (<it>P </it>< 0.05). There was partial sparing of mean post-radiation hearing thresholds at low-to-midrange frequencies and, consequently, the rate of high-grade (grade 3 or 4) ototoxicity at 1 year was favorable (5%). Ototoxicity did not correlate with predicted dose to the auditory apparatus for proton-treated patients, potentially reflecting a lower-limit threshold for radiation effect on the cochlea.</p> <p>Conclusions</p> <p>Rates of high-grade early post-radiation ototoxicity following proton radiotherapy for pediatric medulloblastoma are low. Preservation of hearing in the audible speech range, as observed here, may improve both quality of life and cognitive functioning for these patients.</p

Beta-decay And The Origins Of Biological Chirality - Experimental Results

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62544/1/297639a0.pd

Contemporary Opinions on Intraoperative Facial Nerve Monitoring

Objective To examine the current trend in intraoperative facial nerve monitoring (IOFNM) training, performance, and reimbursement by subspecialists. Study Design Cross-sectional survey of the American Neurotology Society, American Otological Society, American Society of Pediatric Otolaryngology, and program directors of otolaryngology–head and neck surgery programs accredited by the Accreditation Council on Graduate Medical Education. Setting American Academy of Otolaryngology–Head and Neck Surgery Intraoperative Nerve Monitoring Task Force. Subjects and Methods The task force developed 2 surveys, which were implemented through Surveymonkey.com: (1) a 10-question survey sent to 1506 members of the societies listed to determine IOFNM practice and reimbursement patterns and (2) a 10-question survey sent to the 107 accredited US otolaryngology residency program directors to examine the state of resident training on facial nerve monitoring. Results Response rates were 18% for practicing physicians and 15% for residency program directors. The majority agreed that IOFNM was indicated for most otologic and neurotologic procedures. In addition to facial nerve monitoring, facial nerve stimulation was used in complex skull base and temporal bone procedures. When queried about reimbursement by Medicare, only 4.4% of surgeons responded that they received reimbursement. Program directors indicated universal exposure of residents to IOFNM, with 61% of programs giving residents formal training. Conclusions IOFNM is widely used among otologists and neurotologists in the United States. The majority of residents receive formal training, and all residents are exposed to the setup, use, monitoring, and troubleshooting of the device. Reimbursement for IOFNM is reported by a paucity of those surveyed

The combined profunda artery perforator-gracilis flap for immediate facial reanimation and resurfacing of the radical parotidectomy defect

BackgroundA radical parotidectomy with facial nerve sacrifice results in facial nerve paralysis as well as a volume and often cutaneous defect. Prior experience with nerve grafting and static suspension has yielded suboptimal results. The present report aims to examine the feasibility and outcomes of a combined free gracilis and profunda artery perforator (PAP) flap from a single donor site can reconstruct these extensive defects and potentially restore dynamic facial reanimation even in the setting of adjuvant radiation. Patients and MethodsA retrospective review of 10 patients (6 males and 4 females) was performed from 2016 to 2020 that underwent a combined PAP-gracilis reconstruction of a radical parotidectomy defect. All patients (mean age: 71.3 years; range: 52-83 years) received adjuvant radiation. A chimeric PAP-gracilis flap requiring a single microvascular anastomosis was performed in three patients while the remaining patients underwent a double free flap reconstruction. ResultsThe gracilis flap was innervated using the facial nerve stump, spinal accessory and massecteric nerve in three patients each. One patient's gracilis was innervated using the hypoglossal nerve. Three patients also underwent nerve grafting of the facial nerve. One patient was taken back to the operating room for a hematoma in the recipient site and there were not flap losses of either the PAP or gracilis flap. Two patients had delayed wound healing of the donor site that healed with conservative management. Average follow-up was 11.1 months (range: 8.1-19.5 months). Six patients were able to achieve dynamic animation while the others obtained a static reconstruction and did not have issues with drooling, eating, or speaking. ConclusionsImmediate functional muscle transfer can potentially restore dynamic facial reanimation even following radiation. Combining reconstruction using a PAP-gracilis flap addresses the soft tissue deficit and facial paralysis using a single donor site in a single operation