Effects of crack tip geometry on dislocation emission and cleavage: A possible path to enhanced ductility

We present a systematic study of the effect of crack blunting on subsequent crack propagation and dislocation emission. We show that the stress intensity factor required to propagate the crack is increased as the crack is blunted by up to thirteen atomic layers, but only by a relatively modest amount for a crack with a sharp 60$^\circ$ corner. The effect of the blunting is far less than would be expected from a smoothly blunted crack; the sharp corners preserve the stress concentration, reducing the effect of the blunting. However, for some material parameters blunting changes the preferred deformation mode from brittle cleavage to dislocation emission. In such materials, the absorption of preexisting dislocations by the crack tip can cause the crack tip to be locally arrested, causing a significant increase in the microscopic toughness of the crack tip. Continuum plasticity models have shown that even a moderate increase in the microscopic toughness can lead to an increase in the macroscopic fracture toughness of the material by several orders of magnitude. We thus propose an atomic-scale mechanism at the crack tip, that ultimately may lead to a high fracture toughness in some materials where a sharp crack would seem to be able to propagate in a brittle manner. Results for blunt cracks loaded in mode II are also presented.Comment: 12 pages, REVTeX using epsfig.sty. 13 PostScript figures. Final version to appear in Phys. Rev. B. Main changes: Discussion slightly shortened, one figure remove

31st Annual Meeting and Associated Programs of the Society for Immunotherapy of Cancer (SITC 2016) : part two

Background The immunological escape of tumors represents one of the main ob- stacles to the treatment of malignancies. The blockade of PD-1 or CTLA-4 receptors represented a milestone in the history of immunotherapy. However, immune checkpoint inhibitors seem to be effective in specific cohorts of patients. It has been proposed that their efficacy relies on the presence of an immunological response. Thus, we hypothesized that disruption of the PD-L1/PD-1 axis would synergize with our oncolytic vaccine platform PeptiCRAd. Methods We used murine B16OVA in vivo tumor models and flow cytometry analysis to investigate the immunological background. Results First, we found that high-burden B16OVA tumors were refractory to combination immunotherapy. However, with a more aggressive schedule, tumors with a lower burden were more susceptible to the combination of PeptiCRAd and PD-L1 blockade. The therapy signifi- cantly increased the median survival of mice (Fig. 7). Interestingly, the reduced growth of contralaterally injected B16F10 cells sug- gested the presence of a long lasting immunological memory also against non-targeted antigens. Concerning the functional state of tumor infiltrating lymphocytes (TILs), we found that all the immune therapies would enhance the percentage of activated (PD-1pos TIM- 3neg) T lymphocytes and reduce the amount of exhausted (PD-1pos TIM-3pos) cells compared to placebo. As expected, we found that PeptiCRAd monotherapy could increase the number of antigen spe- cific CD8+ T cells compared to other treatments. However, only the combination with PD-L1 blockade could significantly increase the ra- tio between activated and exhausted pentamer positive cells (p= 0.0058), suggesting that by disrupting the PD-1/PD-L1 axis we could decrease the amount of dysfunctional antigen specific T cells. We ob- served that the anatomical location deeply influenced the state of CD4+ and CD8+ T lymphocytes. In fact, TIM-3 expression was in- creased by 2 fold on TILs compared to splenic and lymphoid T cells. In the CD8+ compartment, the expression of PD-1 on the surface seemed to be restricted to the tumor micro-environment, while CD4 + T cells had a high expression of PD-1 also in lymphoid organs. Interestingly, we found that the levels of PD-1 were significantly higher on CD8+ T cells than on CD4+ T cells into the tumor micro- environment (p < 0.0001). Conclusions In conclusion, we demonstrated that the efficacy of immune check- point inhibitors might be strongly enhanced by their combination with cancer vaccines. PeptiCRAd was able to increase the number of antigen-specific T cells and PD-L1 blockade prevented their exhaus- tion, resulting in long-lasting immunological memory and increased median survival

Ultra-thin carbon layer for high density magnetic storage devices

Storage density is presently doubling every year. This requires the read head to approach closer to the magnetic layer, and ever-thinner layers of carbon. Film thickness below 2 nm and roughness well below 1 nm are needed for the storage of ~1 Tb/in2. Here we present an analytical and functional characterisation of ultra-thin carbon nitride and pure carbon films produced by magnetron sputtering and filtered high current vacuum arc. The main focus is the effect of nitrogen com position and decreasing film thickness on the relevant mechanical and tribological properties. The carbon bonding has been monitored by using a combination of Raman spectra, taken at two wavelengths (514 and 244 nm). We show that the density, nitrogen content, scratching resistance and Young's modulus of ultra-thin films can all be monitored by the G peak dispersion. Also, the G peak full width at half maximum is a useful parameter in order to investigate the structural evolution of thin films

Kubisches Bornitrid und Kohlenstoffnitrid - Schichtmaterialien fuer innovative Werkstoffe, magnetische Speicher und Glasprodukte - Herstellung und Pruefung von c-BN und CN_xSchichten fuer die Speichertechnologie Abschlussbericht

SIGLEAvailable from TIB Hannover: F02B53+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman

3

Since its start-up early 1996 KASCADE has collected more than 200 Mio. events with an energy threshold of approx. 10 eV. A unique feature of KASCADE is the simultaneous measurement of electrons, muons, and hadrons at high quality. The large body of data can consistently be described only, if an increasingly heavier composition is assumed above the knee. Quantitatively, subtle differences are identified between hadronic and electromagnetic measurements, with the former pointing to an overall heavier composition. The knee in the primary energy spectrum is observed at E k = 4-5 PeV with a change of the spectral index from fl &apos; 2:7 to 3.1. We critically discuss the preliminary results and point out possible future improvements, particularly in the modeling of EAS

2

The electron and muon numbers of extensive air showers in the energy region around the knee are measured by the detectors of the KASCADE array. To understand the resulting size spectra one has to take into account the fluctuations of the shower development in the atmosphere as well as the uncertainties of the applied reconstruction methods. A consistent interpretation of both spectra allows to derive a primary energy spectrum and a mass composition

He 2.2.41 1

The number of hadrons and their energy sum in extensive air showers has been measured using the KASCADE hadron calorimeter. Shower size spectra of the hadronic component have been derived using both observables. The spectra can be described by a power law and exhibit a change in the spectral index at energies around 5 PeV. The primary cosmic--ray flux spectrum is derived from the measurements in the energy range from 0.2 PeV up to 50 PeV