A multi-color fast-switching microfluidic droplet dye laser

We describe a multi-color microfluidic dye laser operating in whispering gallery mode based on a train of alternating droplets containing solutions of different dyes; this laser is capable of switching the wavelength of its emission between 580 nm and 680 nm at frequencies up to 3.6 kHz -— the fastest among all dye lasers reported; it has potential applications in on-chip spectroscopy and flow cytometry

Cross-link governed dynamics of biopolymer networks

Cytoskeletal networks of biopolymers are cross-linked by a variety of proteins. Experiments have shown that dynamic cross-linking with physiological linker proteins leads to complex stress relaxation and enables network flow at long times. We present a model for the mechanical properties of transient networks. By a combination of simulations and analytical techniques we show that a single microscopic timescale for cross-linker unbinding leads to a broad spectrum of macroscopic relaxation times, resulting in a weak power-law dependence of the shear modulus on frequency. By performing rheological experiments, we demonstrate that our model quantitatively describes the frequency behavior of actin network cross-linked with $\alpha$-Actinin-$4$ over four decades in frequency.Comment: 4 page

Influence of two different resection techniques (conventional liver resection versus anterior approach) of liver metastases from colorectal cancer on hematogenous tumor cell dissemination – prospective randomized multicenter trial

<p>Abstract</p> <p>Background</p> <p>Surgical hepatic resection remains the treatment of choice for patients with liver metastases from colorectal cancer despite the use of alternative therapeutic strategies. Although this procedure provides long-term survival in a significant number of patients, 50–75% of the patients develop intra- and/or extrahepatic recurrence. One possible reason for tumor recurrence may be intraoperative hematogenous tumor cell dissemination due to mechanical manipulation of the tumor during hepatic resection. Surgical technique may have an influence on hematogenous tumor cell spread. We hypothesize that hematogenous tumor cell dissemination may be reduced by using the anterior approach technique compared to conventional liver resection.</p> <p>Methods/Design</p> <p>This is a multi-centre prospective randomized controlled, superiority trial to compare two liver resection techniques of liver metastases from colorectal cancer. 150 patients will be included and randomized intraoperatively after surgical exploration just prior to resection. The primary objective is to compare the anterior approach with the conventional liver resection technique with regard to intraoperative haematogenous tumor cell dissemination. As secondary objectives we examine five year survival rates (OS and DFS), blood loss, duration of operation, requirement of blood transfusions, morbidity rate, prognostic relevance of tumor cell detection in blood and bone marrow and the comparison of tumor cell detection by different detection methods.</p> <p>Conclusion</p> <p>This trial will answer the question whether there is an advantage for the anterior approach technique compared to the conventional resection group with regard to tumor cell dissemination. It will also add further information about prognostic differences, safety, advantages and disadvantages of each technique.</p> <p>Trial registration</p> <p>Current controlled trials – <b>ISRCTN45066244</b></p

X-ray dark-field tomography reveals tooth cracks

Abstract Cracked tooth syndrome (CTS) is a common clinical finding for teeth, it affects about 5% of all adults each year. The finding of CTS is favored by several risk factors such as restorations, bruxism, occlusion habits, and age. Treatment options range, depending on the severity, from no treatment at all to tooth extraction. Early diagnosis of CTS is crucial for optimal treatment and symptom reduction. There is no standard procedure for an evidence-based diagnosis up to date. The diagnosis is a challenge by the fact that the symptoms, including pain and sensitivity to temperature stimuli, cannot be clearly linked to the disease. Commonly used visual inspection does not provide in-depth information and is limited by the resolution of human eyes. This can be overcome by magnifying optics or contrast enhancers, but the diagnosis will still strongly rely on the practicians experience. Other methods are symptom reproduction with percussions, thermal pulp tests or bite tests. Dental X-ray radiography, as well as computed tomography, rarely detect cracks as they are limited in resolution. Here, we investigate X-ray dark-field tomography (XDT) for the detection of tooth microcracks. XDT simultaneously detects X-ray small-angle scattering (SAXS) in addition to the attenuation, whereas it is most sensitive to the micrometer regime. Since SAXS originates from gradients in electron density, the signal is sensitive to the sample morphology. Microcracks create manifold interfaces which lead to a strong signal. Therefore, it is possible to detect structural changes originating from subpixel-sized structures without directly resolving them. Together with complementary attenuation information, which visualizes comparatively large cracks, cracks are detected on all length-scales for a whole tooth in a non-destructive way. Hence, this proof-of principle study on three ex-vivo teeth shows the potential of X-ray scattering for evidence-based detection of cracked teeth

Production of Sodium Bose--Einstein condensates in an optical dimple trap

We report on the realization of a sodium Bose--Einstein condensate (BEC) in a combined red-detuned optical dipole trap, formed by two beams crossing in a horizontal plane and a third, tightly focused dimple trap propagating vertically. We produce a BEC in three main steps: loading of the crossed dipole trap from laser-cooled atoms, an intermediate evaporative cooling stage which results in efficient loading of the auxiliary dimple trap, and a final evaporative cooling stage in the dimple trap. Our protocol is implemented in a compact setup and allows us to reach quantum degeneracy even with relatively modest initial atom numbers and available laser power

Valley splitting of Si/SiGe heterostructures in tilted magnetic fields

We have investigated the valley splitting of two-dimensional electrons in high quality Si/Si$_{1-x}$Ge$_x$ heterostructures under tilted magnetic fields. For all the samples in our study, the valley splitting at filling factor $\nu=3$ ($\Delta_3$) is significantly different before and after the coincidence angle, at which energy levels cross at the Fermi level. On both sides of the coincidence, a linear density dependence of $\Delta_3$ on the electron density was observed, while the slope of these two configurations differs by more than a factor of two. We argue that screening of the Coulomb interaction from the low-lying filled levels, which also explains the observed spin-dependent resistivity, is responsible for the large difference of $\Delta_3$ before and after the coincidence.Comment: REVTEX 4 pages, 4 figure

Arbitrary rotation and entanglement of flux SQUID qubits

We propose a new approach for the arbitrary rotation of a three-level SQUID qubit and describe a new strategy for the creation of coherence transfer and entangled states between two three-level SQUID qubits. The former is succeeded by exploring the coupled-uncoupled states of the system when irradiated with two microwave pulses, and the latter is succeeded by placing the SQUID qubits into a microwave cavity and used adiabatic passage methods for their manipulation.Comment: Accepted for publication in Phys. Rev.

Valley Splitting Theory of SiGe/Si/SiGe Quantum Wells

We present an effective mass theory for SiGe/Si/SiGe quantum wells, with an emphasis on calculating the valley splitting. The theory introduces a valley coupling parameter, $v_v$, which encapsulates the physics of the quantum well interface. The new effective mass parameter is computed by means of a tight binding theory. The resulting formalism provides rather simple analytical results for several geometries of interest, including a finite square well, a quantum well in an electric field, and a modulation doped two-dimensional electron gas. Of particular importance is the problem of a quantum well in a magnetic field, grown on a miscut substrate. The latter may pose a numerical challenge for atomistic techniques like tight-binding, because of its two-dimensional nature. In the effective mass theory, however, the results are straightforward and analytical. We compare our effective mass results with those of the tight binding theory, obtaining excellent agreement.Comment: 13 pages, 7 figures. Version submitted to PR

Gelation as arrested phase separation in short-ranged attractive colloid-polymer mixtures

We present further evidence that gelation is an arrested phase separation in attractive colloid-polymer mixtures, based on a method combining confocal microscopy experiments with numerical simulations recently established in {\bf Nature 453, 499 (2008)}. Our results are independent of the form of the interparticle attractive potential, and therefore should apply broadly to any attractive particle system with short-ranged, isotropic attractions. We also give additional characterization of the gel states in terms of their structure, inhomogeneous character and local density.Comment: 6 figures, to be published in J. Phys. Condens. Matter, special issue for EPS Liquids Conference 200