Low-temperature low-field phases of the pyrochlore quantum magnet Tb2Ti2O7

By means of ac magnetic-susceptibility measurements, we find evidence for a new magnetic phase of Tb2Ti2O7 below about 140 mK in zero magnetic field. In magnetic fields parallel to [111], this phase is characterized by frequency- and amplitude-dependent susceptibility and extremely slow spin dynamics. In the zero-temperature limit, it extends to about 67 mT (the internal field H(int)≃52  mT), at which it makes transition to another phase. The field dependence of the susceptibility of this second phase, which extends to about 0.60 T (H(int)≃0.54  T) in the zero-temperature limit, indicates the presence of a weak magnetization plateau below about 50 mK, as has been predicted by a single-tetrahedron four-spin model, suggesting that the second phase is a quantum kagome ice.

Self-organized bursts of coherent stimulated Raman scattering and hot electron transport in speckled laser plasma media

Nonlinear electron trapping physics governs the onset and saturation of stimulated Raman scattering (SRS) in laser beams with many speckles. Hot electrons from intense speckles, produced during SRS daughter electron-plasma-wave bowing and filamentation, seed and enhance the growth of SRS in neighboring speckles by reducing Landau damping. Trapping-induced nonlinearity and speckle interaction through transport of hot electrons and back- and sidescattered SRS waves enable the system of speckles to self-organize and exhibit coherent, sub-ps SRS bursts with more than 100% instantaneous reflectivity, consistent with a SRS transverse coherence width much larger than a speckle width.

SU-E-J-19: How Should CTV to PTV Margin Be Created - Analysis of Set-Up Uncertainties of Different Body Parts Using Daily Image Guidance

PURPOSE

The objective for this study is to systematically evaluate how the CTV to PTV margin should be created to compensate for setup error as afunction of treatment site.

METHODS

A total of 1757 setup MVCT images were analyzed using the registration between the MVCT and planning KVCT images. Among them, 526 images were from patients with head and neck cancers; 342 were from thoracic site; 447 from upper abdomen and 442 from patients treated at pelvic region. The correction was shifts in 3 directions from setup with skin marks to final treatment position due to volumetric image registration. Registration was based on soft tissue anatomy when tumor was visible in both KVCT and MVCT. Otherwise, bony landmarks were used when tumors could not be identified.

RESULTS

The anterior to posterior (A/P) direction requires the smallest correction for all body sites. The percentage of treatment with < 3mm set-up correction in A/P direction was 82.4%-96.0% for all disease sites. In medial to lateral direction (M/L), that number was 51.5%-74.7%. The largest set-up correction occurred in the superior to inferior (S/I) direction. As a function of the body site, 68.6% of head and neck patient had <3mm shift in the S/I direction. However, that number dropped to 41.8%〠42.5% and 31.9% for thoracic, upper abdomen and pelvic sites respectively. In addition, 48.0% of pelvic tumor required >5mm shift in the S/I direction. For thoracic and abdominal tumors, there were still 34.9% and 30.7% of the treatments where >5mm shift in the S/I direction was needed.

CONCLUSIONS

Uniform expansion margins in all directions are often used in radiation oncology practice. Our study showed setup error was directionally dependent. Therefore, non-uniform margin should be applied. Smaller margin can be used in A/P while larger expansion needs to be given in the S/I direction.

ROBUSTNESS, STABILITY AND EFFICIENCY OF PHAGE λ GENETIC SWITCH: DYNAMICAL STRUCTURE ANALYSIS

Based on the dynamical structure theory for complex networks recently developed by one of us and on the physical-chemical models for gene regulation, developed by Shea and Ackers in the 1980's, we formulate a direct and concise mathematical framework for the genetic switch controlling phage λ life cycles, which naturally includes the stochastic effect. The dynamical structure theory states that the dynamics of a complex network is determined by its four elementary components: The dissipation (analogous to degradation), the stochastic force, the driving force determined by a potential, and the transverse force. The potential may be interpreted as a landscape for the phage development in terms of attractive basins, saddle points, peaks and valleys. The dissipation gives rise to the adaptivity of the phage in the landscape defined by the potential: The phage always has the tendency to approach the bottom of the nearby attractive basin. The transverse force tends to keep the network on the equal-potential contour of the landscape. The stochastic fluctuation gives the phage the ability to search around the potential landscape by passing through saddle points.

With molecular parameters in our model fixed primarily by the experimental data on wild-type phage and supplemented by data on one mutant, our calculated results on mutants agree quantitatively with the available experimental observations on other mutants for protein number, lysogenization frequency, and a lysis frequency in lysogen culture. The calculation reproduces the observed robustness of the phage λ genetic switch. This is the first mathematical description that successfully represents such a wide variety of major experimental phenomena. Specifically, we find: (1) The explanation for both the stability and the efficiency of phage λ genetic switch is the exponential dependence of saddle point crossing rate on potential barrier height, a result of the stochastic motion in a landscape; and (2) The positive feedback of cI repressor gene transcription, enhanced by the CI dimer cooperative binding, is the key to the robustness of the phage λ genetic switch against mutations and fluctuations in kinetic parameter values.

Protease inhibitor levels in periodontal health and disease

BACKGROUND AND OBJECTIVE

Our previous study showed that protease inhibitors were attenuated by the periodontal pathogen Porphyromonas gingivalis in cultured gingival epithelial cells. We hypothesize that fewer protease inhibitors would be present in more advanced periodontal disease sites, where the level of P. gingivalis may be high. The goal of this study was to investigate the relationship between the protease inhibitor [secretory leukocyte protease inhibitor (SLPI), elastase-specific inhibitor (ELAFIN) and squamous cell carcinoma antigen (SCCA)] levels in gingival crevicular fluid and the number of P. gingivalis micro-organisms in subgingival plaque.

MATERIAL AND METHODS

Plaque samples from subjects without (n = 18) and with moderate to advanced periodontitis (n = 41) were used to quantify P. gingivalis using real-time PCR. Protease inhibitor levels in the gingival crevicular fluid of all the subjects were determined by ELISA.

RESULTS

P. gingivalis was detected in 68.3% of patients with periodontitis, while 16.7% of subjects without periodontitis had a detectable level of P. gingivalis. Patients with periodontitis and P. gingivalis in their plaque exhibited lower SLPI and ELAFIN levels (p < 0.001) compared with control subjects without periodontitis. Secretory leukocyte protease inhibitor was also reduced (p < 0.05) in gingival crevicular fluid of periodontitis patients without a detectable level of P. gingivalis. Periodontitis patients with high vs. low levels of P. gingivalis exhibited reciprocal mean levels of SLPI and ELAFIN concentrations.

CONCLUSION

The reduced concentrations of SLPI and ELAFIN may contribute to the loss of host protective capacity and increase susceptibility to breakdown from chronic infection. The work of this investigation may aid in finding diagnostic and prognostic markers in periodontal health and disease and may also help in finding pharmacological targets directed against periodontal inflammation.