[en] We have collected neutron diffraction data on a large single crystal of the title compound. The most surprising result is an extremely short Rh-H distance of 1.31(8) A, presumably caused by steric interactions involving the bulky triphenyl phosphine ligands. Crystallographic details: HRh[P(C₆H₅)₃]₄ . ¹/₂C₆H₆ crystallizes in the space group Pa3, with a = b = c = 22.776(3) A, Z = 8. Data were collected at the Brookhaven High Flux Beam reactor at a temperature of -23⁰C, λ = 1.15882(7) A^-1. Least-squares refinement (in which the phenyl rings were treated as rigid groups) resulted in an R factor [based on data with f > 4σ(F)] of 0.12 for 914 reflections and 95 parameters. 10 refs

[en] For radiotherapy, an error in the complicated treatment planning or treatment procedure is a possibility, however remote. Thus, in the present study electron spin resonance (ESR) in dental enamel was investigated for the first time as a means of retrospective dosimetry for validating applied radiotherapy doses to the head and neck regions. Total absorbed radiation doses measured by ESR in dental enamel were compared to the doses determined by treatment planning for 19 patients who received radiotherapy for intra-oral, pharyngeal or laryngeal malignancies, or total-body irradiation prior to bone marrow transplants (BMT). For the 15 tumour irradiations there was, within the framework of the tooth positions as presented, general agreement between the treatment planned and ESR dose determinations. There were, however, both significant and minor discrepancies. For the BMT patients there were major discrepancies for two of the four patients investigated. This study indicates that ESR in dental enamel may be useful as the only means of retrospective dosimetry for validating applied radiotherapy doses after treatment. However, further research must be carried out before this technique can be accepted as accurate and reliable. (author)

[en] The NIF and LMJ laser systems require about 3380 and 4752 Nd-doped laser glass slabs, respectively. Continuous laser glass melting and forming will be used for the first time to manufacture these slabs. Two vendors have been chosen to produce the glass: Hoya Corporation and Schott Glass Technologies. The laser glass melting systems that each of these two vendors have designed, built and tested are arguably the most advanced in the world. Production of the laser glass will begin on a pilot scale in the fall of 1999

[en] Purpose: To examine the effects of an increased dose of radiation therapy (RT) delivered by a hyperfractionated schedule compared to conventional once daily RT on toxicity, locoregional control and survival in the treatment of squamous cell carcinomas (SCC) of the larynx and pharynx. Materials/Methods: Between 1988 and 1995 336 patients were randomized to receive RT with curative intent. Eligible patients had biopsy proven SCC of the larynx or pharynx, with TN stages (AJC-UICC 1987) T3 or T4 N0, or any T with any N+. All patients were M0. Patients were stratified by site (larynx/oropharynx/hypopharynx), node status (clinically positive/negative), and performance status. Patients were treated with either 51 Gy TAD/20 fractions/4 wk (2.55 Gy 1x/d, conventional RT=CRT) or 58 Gy TAD/40 fractions/4 wk (1.45 Gy 2x/d, hyperfractionated RT=HFRT). Patients underwent EUA and selective biopsies 10 wk after RT; surgical salvage was performed for residual or recurrent cancer whenever possible. Results: The primary cancer arose in the oropharynx (138), larynx (133) or hypopharynx (65). T stages were distributed T1 22, T2 72, T3 133 and T4 109. N stage distribution was N0 127, N1 74, N2 117 and N3 18. The proportion of patients with acute mucosal toxicity (RTOG Grade 3 or 4) was increased by HFRT (60% versus 40%), but other acute and late toxicity was not significantly different. There was no difference in the incidence of morbidity in the two treatment groups in those who underwent surgery following RT. The locoregional control rates at 3 yrs for all cases were 45% (HFRT) vs 40% (CRT) log rank p=0.16; for primary tumors <4 cm 54% (HFRT) vs 42% (CRT) p=0.04; for primary tumors ≥ 4 cm 38% (HFRT) vs 41% (CRT) p=0.73. Local control was improved to some extent in SCC which arose in all sites, but most noticeably in hypopharyngeal cancers. The disease free survival rates at 3 yr for all cases were 37% (HFRT) vs 30% (CRT) p=0.15; for primary tumors < 4 cm 47% (HFRT) vs 34% (CRT) p=0.10; for primary tumours ≥ 4 cm 31% (HFRT) vs 29% (CRT) p=0.88. Conclusion: The HFRT schedule used was tolerable and resulted in significantly improved locoregional control at 3 yr in patients with primary SCC less than 4 cm in size. Followup continues to determine whether this advantage is maintained and to monitor late toxicity

[en] Purpose: Pretreatment hemoglobin (Hb) level has been reported to be an important prognostic factor for local control and survival in various malignancies. However in many settings, the adverse effect of a low Hb may be related to more advanced disease and the purpose of this analysis was to assess the influence of pretreatment Hb on local control in a large series of patients with a localised cancer (T1/T2 glottic cancer, AJCC 1992) treated in a standard fashion. Materials and Methods: Between Jan 1981 and Dec 1989, 735 patients (median age 63, 657 males 78 females) with T1/T2 glottic cancer were treated with RT. The standard RT prescription was 50Gy in 20 fractions over 4 weeks (97% patients). Factors studied for prognostic importance for local failure included pretreatment Hb (assessed as a continuous variable) age, sex, T category, anterior commissure involvement, subglottic extension, tumour bulk (presence of visible tumour vs subclinical disease), treatment time and RT technique (Cobalt vs 6 MV). Results: With a median follow-up of 6.8 years (range 0.2 - 14.3), 131 patients have relapsed for an actuarial 5-year relapse free rate of 81.7%. The 5-year actuarial survival was 75.8%, cause specific survival - 92.4%. The median pretreatment hemoglobin level was 14.8 g/dl and was the same in all T categories. On multivariate analysis, using the Cox proportional hazards model, pretreatment Hb (p=0.001) predicted for local failure after RT. The relative risk (RR) for relapse was calculated for various Hb levels eg the RR for a Hb of 12 g/dl vs a Hb of 15 g/dl was 1.8, (95% C.I. 1.3 - 2.7). Previously noted factors including gender (p=0.0038), T category (p=0.007)) as well as tumour bulk (p=0.02) were also prognostically important for local control. Conclusions: This analysis, in a large number of similarly treated patients, indicates that pretreatment Hb is an independent prognostic factor for local control in patients with T1/T2 carcinoma of the glottis treated with RT. The underlying biology of this observation needs to be explored and using this information it may be possible to develop strategies to improve treatment outcome

[en] Purpose/Objective: Radiation-induced xerostomia is a frequent cause of morbidity in head and neck cancer patients. To minimize this complication unilateral techniques (UT) designed to treat the primary tumor and ipsilateral neck have been used for many years in selected cases at our institution. Although such techniques exclude the contralateral parotid from the high dose target volume, they also leave the contralateral neck nodes untreated. The purpose of the study was to evaluate the risk of failure in the opposite neck. Materials and Methods: We identified 229 patients treated with UT from a series of 641 cases with carcinoma of the tonsillar region treated with curative intent between 1970 and 1991. Detailed documentation of the tumor, the radiation dosimetry, the sites of failure, and outcome including local, regional, and distant failure, and late complications, were performed. Actuarial 5-year plots were used to calculate local control, regional control, and survival rates. Results: Median age was 61 years (74 females/155 males); median follow-up 8 years (range 6 months to 21 years). AJCC (1992) T categories were T1:73, T2:120, T3:30, T4:6. The N category distribution was: N0:136, N1:53, N2a:29, N2b:8, and N3:8 cases. Base of tongue and palate were involved in 49 and 82 cases respectively. Irradiation techniques consisted of ipsilateral wedge pairs with Cobalt of 6MV photons in 210 cases (92%), while the remainder were electrons with or without photons. Customized compensators were used in the majority of cases in addition to the use of wedge filters. 75% received 50 Gy in 4 weeks, 10% received 60 Gy in 6 weeks, while the remainder received other doses intended to be curative. A radioactive implant was also used in 20 patients. The 5-year actuarial rates were as follows: overall local control: 76%, regional node control: 80%; cause specific survival: 80%. A total of 7 patients manifested regional disease in the opposite neck (crude rate of 3% or 7 of 229). Of these, 3 had T3 lesions and 4 had T2 lesions. In 4 of the 7, the primary failed prior to or concurrent with the neck failure. The remaining 3 patients had isolated contralateral failure and all three had extensive initial soft palate involvement (to within 1 cm of mid-line in two cases). One of the three also had extensive tongue base involvement. Severe late toxicity was uncommon. Osteoradionecrosis requiring surgery was seen in 3% of patients (7 of 229) but was only seen once in the series after 1983. This is likely due to the introduction of a preventative maintenance dental program Conclusion: This analysis indicates that in appropriately selected cases the risk of failure in the opposite neck is uncommon with UT. We would advise caution for higher radiotherapy doses where toxicity may be arise from technical dose inhomogeneity with wedged pair photon fields and multiple field plans to the ipsilateral side may then be preferable. These results are comparable to the results of bilateral radiation techniques in the literature and suggest that permanent xerostomia may be avoided in selected cases of carcinoma of the tonsillar region

[en] We have collected neutron diffraction data on a large single crystal of the title compound. The most surprising result is an extremely short Rh-H distance of 1.3(8) A, possibly caused by steric interactions involving the bulky triphenyl phosphine ligands. Crystallographic details: HRh[P(C₆H₅)₃]₄.1/2C₆H₆ crystallizes in the cubic space group Pa3, with a₀ = 22.776(3) A, Z = 8. Data were collected at the Brookhaven High Flux Beam reactor at a temperature of -23 degrees C, λ = 1.15882(7) A. Least-squares refinement (in which the phenyl rings were treated as rigid groups) resulted in an R factor [based on data with F > 4σ(F)] of 0.12 for 914 reflections and 95 parameters. (author) 12 refs., 1 fig

[en] We present a new radio survey of about 100 late-M and L dwarfs undertaken with the Very Large Array. The sample was chosen to explore the role of rotation in the radio activity of ultracool dwarfs. As part of the survey we discovered radio emission from three new objects, 2MASS J 0518113 – 310153 (M6.5), 2MASS J 0952219 – 192431 (M7), and 2MASS J 1314203 + 132001 (M7), and made an additional detection of LP 349-25 (M8). Combining the new sample with results from our previous studies and from the literature, we compile the largest sample to date of ultracool dwarfs with radio observations and measured rotation velocities (167 objects). In the spectral type range M0-M6 we find a radio activity-rotation relation, with saturation at L_rad/L_bol ≈ 10^–7.5 above vsin i ≈ 5 km s^–1, similar to the relation in Hα and X-rays. However, at spectral types ∼> M7 the ratio of radio to bolometric luminosity increases significantly regardless of rotation velocity, and the scatter in radio luminosity increases. In particular, while the most rapid rotators (vsin i ∼> 20 km s^–1) exhibit 'super-saturation' in X-rays and Hα, this effect is not seen in the radio. We also find that ultracool dwarfs with vsin i ∼> 20 km s^–1 have a higher radio detection fraction by about a factor of three compared to objects with vsin i ∼< 10 km s^–1. When measured in terms of the Rossby number (Ro), the radio activity-rotation relation follows a single trend and with no apparent saturation from G to L dwarfs and down to Ro ∼ 10^–3; in X-rays and Hα there is clear saturation at Ro ∼< 0.1, with super-saturation beyond M7. A similar trend is observed for the radio surface flux (L_rad/R²_*) as a function of Ro. The continued role of rotation in the overall level of radio activity and in the fraction of active sources, and the single trend of L_rad/L_bol and L_rad/R²_* as a function of Ro from G to L dwarfs, indicates that rotation effects are important in regulating the topology or strength of magnetic fields in at least some fully convective dwarfs. The fact that not all rapid rotators are detected in the radio provides additional support to the idea of dual dynamo states proposed from spectropolarimetric observations.

[en] The effects of solid solution and oxide dispersion alloying on viscoelastic relaxation behavior of Au alloy films were investigated by using gas pressure bulge testing in the temperature range of 20–80 °C. Three sets of 500 nm thick films were fabricated for the study: nominally pure Au, Au-V solid solution alloys with V concentration ranging from 0.89 to 5.4 at% V, and a Au-V₂O₅ nanoparticle dispersion alloy with a V concentration of 5.4 at%. The residual stress, unrelaxed plane strain modulus, and normalized time-dependent effective modulus were determined as a function of alloy type and temperature. Both alloying approaches resulted in a refined grain size that was thermally stable. As expected, the fractional modulus decay measured after 3 h was greater at higher temperatures for all cases. Solid solution strengthening and dispersion strengthening were both effective at reducing the 3-h modulus decay, and the Au-V₂O₅ films showed the largest resistance to relaxation at all temperatures studied. Activation energy analysis reveals a value of approximately 0.11 eV, matching the Peierls barrier height, for pure Au and the two alloys. The results are consistent with a viscoelastic stress relaxation mechanism based on reversible dislocation bowing, weak solid solution hardening through elastic solute/dislocation interactions, and strong dislocation pinning associated with oxide nanoparticles.

[en] We present multi-epoch radio and optical observations of the M7 dwarf 2MASS J13142039+1320011. We detect a ∼1 mJy source at 1.43, 4.86, 8.46, and 22.5 GHz, making it the most luminous radio emission over the widest frequency range detected from an ultracool dwarf to date. A 10 hr Very Large Array observation reveals that the radio emission varies sinusoidally with a period of 3.89 ± 0.05 hr, and an amplitude of ∼30% at 4.86 GHz and ∼20% at 8.46 GHz. The periodicity is also seen in circular polarization, where at 4.86 GHz the polarization reverses helicity from left- to right-handed in phase with the total intensity. An archival detection in the Faint Images of the Radio Sky at Twenty Centimeters survey indicates that the radio emission has been stable for at least a decade. We also detect periodic photometric variability in several optical filters with a period of 3.79 hr and measure a rotation velocity of vsin i = 45 ± 5 km s^-1, in good agreement with the radio and optical periods. The subtle difference in radio and optical periods may be due to differential rotation, with ΔΩ ∼ 1 rad day^-1 between the equation and poles. The period and rotation velocity allow us to place a lower limit on the radius of the source of ∼> 0.13R_sun, about 30% larger than theoretical expectations. The properties of the radio emission can be explained with a simple model of a magnetic dipole misaligned relative to the stellar rotation axis, with the sinusoidal variations and helicity reversal due to the rotation of the magnetic poles relative to our line of sight. The long-term stability of the radio emission indicates that the magnetic field (and hence the dynamo) is stable on a much longer timescale than the convective turnover time of ∼0.2 yr. If the radio emission is due to gyrosynchrotron emission the inferred magnetic field strength is ∼0.1 kG, while the electron cyclotron maser process requires a field of at least 8 kG.