Thermodynamic first order transition and inverse freezing in a 3D spin-glass

We present a numerical study of the random Blume-Capel model in three dimension. The phase diagram is characterized by spin-glass/paramagnet phase transitions both of first and second order in the thermodynamic sense. Numerical simulations are performed using the Exchange-Monte Carlo algorithm, providing clear evidence for inverse freezing. The main features at criticality and in the phase coexistence region are investigated. We are not privy to other 3D short-range systems with quenched disorder undergoing inverse freezing.Comment: 4 pages, 3 figures

Probing the Debye spectrum in glasses using small system sizes

The work aims to show that small system sizes in numerical simulations turns out to be useful for investigating the Debye spectrum in glasses

Generalized energy equipartition in harmonic oscillators driven by active baths

We study experimentally and numerically the dynamics of colloidal beads confined by a harmonic potential in a bath of swimming E. coli bacteria. The resulting dynamics is well approximated by a Langevin equation for an overdamped oscillator driven by the combination of a white thermal noise and an exponentially correlated active noise. This scenario leads to a simple generalization of the equipartition theorem resulting in the coexistence of two different effective temperatures that govern dynamics along the flat and the curved directions in the potential landscape.Comment: 4 pages, 3 figure

Probing the non-Debye low frequency excitations in glasses through random pinning

We investigate the properties of the low-frequency spectrum in the density of states $D(\omega)$ of a three-dimensional model glass former. To magnify the Non-Debye sector of the spectrum, we introduce a random pinning field that freezes a finite particle fraction in order to break the translational invariance and shifts all the vibrational frequencies of the extended modes towards higher frequencies. We show that Non-Debye soft localized modes progressively emerge as the fraction $p$ of pinned particles increases. Moreover, the low-frequency tail of $D(\omega)$ goes to zero as a power law $\omega^{\delta(p)}$, with $2 \!\leq \! \delta(p) \!\leq\!4$ and $\delta\!=\!4$ above a threshold fraction $p_{th}$.Comment: 4 Figures, submitted to PNA

Colloidal transport by light induced gradients of active pressure

The mechanical forces exerted by active fluids may provide an effective way of transporting microscopic objects, but the details remain elusive. Using space modulated activity, Pellicciotta et al. generate active pressure gradients capable of transporting passive particles in controlled directions.Active fluids, like all other fluids, exert mechanical pressure on confining walls. Unlike equilibrium, this pressure is generally not a function of the fluid state in the bulk and displays some peculiar properties. For example, when activity is not uniform, fluid regions with different activity may exert different pressures on the container walls but they can coexist side by side in mechanical equilibrium. Here we show that by spatially modulating bacterial motility with light, we can generate active pressure gradients capable of transporting passive probe particles in controlled directions. Although bacteria swim faster in the brighter side, we find that bacteria in the dark side apply a stronger pressure resulting in a net drift motion that points away from the low activity region. Using a combination of experiments and numerical simulations, we show that this drift originates mainly from an interaction pressure term that builds up due to the compression exerted by a layer of polarized cells surrounding the slow region. In addition to providing new insights into the generalization of pressure for interacting systems with non-uniform activity, our results demonstrate the possibility of exploiting active pressure for the controlled transport of microscopic objects

Alignment interactions drive structural transitions in biological tissues

Experimental evidence shows that there is a feedback between cell shape and cell motion. How this feedback impacts the collective behavior of dense cell monolayers remains an open question. We investigate the effect of a feedback that tends to align the cell crawling direction with cell elongation in a biological tissue model. We find that the alignment interaction promotes nematic patterns in the fluid phase that eventually undergo a nonequilibrium phase transition into a quasihexagonal solid. Meanwhile, highly asymmetric cells do not undergo the liquid-to-solid transition for any value of the alignment coupling. In this regime, the dynamics of cell centers and shape fluctuation show features typical of glassy systems

Regenerating Articular Tissue by Converging Technologies

Scaffolds for osteochondral tissue engineering should provide mechanical stability, while offering specific signals for chondral and bone regeneration with a completely interconnected porous network for cell migration, attachment, and proliferation. Composites of polymers and ceramics are often considered to satisfy these requirements. As such methods largely rely on interfacial bonding between the ceramic and polymer phase, they may often compromise the use of the interface as an instrument to direct cell fate. Alternatively, here, we have designed hybrid 3D scaffolds using a novel concept based on biomaterial assembly, thereby omitting the drawbacks of interfacial bonding. Rapid prototyped ceramic particles were integrated into the pores of polymeric 3D fiber-deposited (3DF) matrices and infused with demineralized bone matrix (DBM) to obtain constructs that display the mechanical robustness of ceramics and the flexibility of polymers, mimicking bone tissue properties. Ostechondral scaffolds were then fabricated by directly depositing a 3DF structure optimized for cartilage regeneration adjacent to the bone scaffold. Stem cell seeded scaffolds regenerated both cartilage and bone in vivo

Phase I/II trial of gemcitabine plus cisplatin and etoposide in patients with small-cell lung cancer

Objective: The objectives of this phase 1/11 study were to define the maximum tolerated dose (MTD), safety, and activity of cisplatin, etoposide, and gemcitabine (PEG) in the treatment of previously untreated patients with small-cell lung cancer (SCLC). Patients and Methods: Chemonaive patients received fixed doses of gemcitabine (1000 mg/m(2) on days I and 8) and cisplatin (70 mg/m(2) on day 2) and escalating doses of etoposide (starting dose of 50 mg/m(2) on days 3,4, and 5) every 3 weeks. No prophylactic granulocyte colony-stimulating factors were used. Results: From September 1998 to April 2000, 56 patients with limited- or extensive-stage SCLC were enrolled and received a total of 235 cycles. Two different etoposide doses were tested in eight patients. At the second level (75 mg/m(2)), two out of two patients experienced dose-limiting toxicities (neutropenia and thrombocytopenia) and no further dose-escalation was attempted, thus an etoposide dose of 50 mg/m 2 was defined as the MTD. In the subsequent phase 11 evaluation, 48 additional patients were enrolled, for a total of 54 patients treated at the MTD. Grade 3/4 neutropenia and thrombocytopenia occurred in 66.7 and 53.7%,, of patients, respectively. Non-hematologic toxicity was mild, with grade 3 diarrhea and fatigue as the main side effects. Two patients died of neutropenic sepsis (one at 75 mg/m(2) and the other at So I n g/In 2 etoposide). Ten complete and 29 partial responses were reported, for an overall response rate of 72.2% (95% confidence interval, 56.6-85.0%). The median duration of response and median survival were 8.0 and 10 months, respectively, with a 1-year survival probability of 37.5%. Conclusions: he combination of PEG is feasible and well tolerated as front-line chemotherapy in SCLC. A randomized comparison of this triplet is underway. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved