Spontaneous Symmetry Breaking for Driven Interacting Particles on Triangular Substrates

For collectively interacting repulsive particles driven on triangular substrates, we show that for certain directions of drive a spontaneous symmetry breaking phenomena occurs where the particles can flow in one of two directions that are not aligned with the external drive, giving rise to a positive or negative Hall current. Along these directions, the particle flow is highly ordered, while in the direction of the drive the flow is disordered. We also find a number of dynamical phase transitions and unusual hysteretic properties that arise due to the symmetry breaking properties of the flows.Comment: 4 pages, 4 postscript figure

Manipulation and assembly of nanowires with holographic optical traps

We demonstrate that semiconductor nanowires measuring just a few nanometers in diameter can be translated, rotated, cut, fused and organized into nontrivial structures using holographic optical traps. The holographic approach to nano-assembly allows for simultaneous independent manipulation of multiple nanowires, including relative translation and relative rotation.Comment: 5 pages, 5 figure

Holographic optical trapping

Holographic optical tweezers use computer-generated holograms to create arbitrary three-dimensional configurations of single-beam optical traps useful for capturing, moving and transforming mesoscopic objects. Through a combination of beam-splitting, mode forming, and adaptive wavefront correction, holographic traps can exert precisely specified and characterized forces and torques on objects ranging in size from a few nanometers to hundreds of micrometers. With nanometer-scale spatial resolution and real-time reconfigurability, holographic optical traps offer extraordinary access to the microscopic world and already have found applications in fundamental research and industrial applications.Comment: 8 pages, 7 figures, invited contribution to Applied Optics focus issue on Digital Holograph

Antibiotic sensitivity of enterobacteriaceae

Enterobakterije su važni uzročnici infekcija mokraćnog sustava (IMS), infekcija probavnog sustava te infekcija povezanih sa zdravstvenom skrbi. Pri odabiru empirijske antimikrobne terapije treba voditi računa o intrinzičnoj otpornosti nekih bakterijskih vrsta na određene grupe antibiotika, ali još veći problem predstavljaju brojni, stalno mijenjajući, mehanizmi stečene otpornosti na antibiotike. Beta-laktamski antibiotici su najčešće upotrebljavani antibiotici u kliničkoj praksi, a trimetoprim-sulfametoksazol (ko-trimoksazol) i kinoloni su dragocjeni u liječenju IMS i infekcija probavnog sustava, jer uspješno eradiciraju patogene iz ovih sustava. Na sve nabrojene grupe antibiotika javljaju se, međutim, mnogi mehanizmi otpornosti, koji često djeluju udruženo u istom bakterijskom soju. U Hrvatskoj otpornost E. coli iznosi 3% na III. generaciju cefalosporina, 24% na ko-trimoksazol te 11% na ciprofloksacin. K. pneumoniae je češće uzročnik infekcija povezanih sa zdravstvenom skrbi i pokazuje viši stupanj otpornosti na antibiotike; 29% na III. generaciju cefalosporina te 36% na ko-trimoksazol i ciprofloksacin. U Hrvatskoj otpornost enterobakterija na karbapeneme je još uvijek sporadična.Enterobacteriaceae are important pathogens in urinary tract infections (UTI), gastrointestinal and healthcare associated infections. When deciding on empirical antibiotic therapy intrinsic resistance mechanisms present in certain bacterial species should be considered but even more worrisome problem is the presence of numerous, always changing, mechanisms of acquired resistance. Beta-lactam antibiotics are the most frequently used antibiotics in clinical practice and trimethoprim-sulfamethoxazole (co-trimoxazole) and the quinolones are precious drugs in the treatment of UTI and gastrointestinal infections due to their ability to eradicate pathogens from these sites. Numerous resistance mechanisms have emerged to all these groups of antibiotics and often different mechanisms are present in the same strain. In Croatia, E. coli isolates resistance rates are 3% for the 3rd generation cephalosporins, 24% for co-trimoxazole and 11% for ciprofloxacin. K. pneumoniae more often causes healthcare associated infections and has higher rates of resistance; 29% for 3rd generation cephalosporins and 36% for co-trimoxazole and ciprofloxacin. In Croatia carbapenem resistance in enterobacteriaceae is still sporadic

Colloidal hydrodynamic coupling in concentric optical vortices

Optical vortex traps created from helical modes of light can drive fluid-borne colloidal particles in circular trajectories. Concentric circulating rings of particles formed by coaxial optical vortices form a microscopic Couette cell, in which the amount of hydrodynamic drag experienced by the spheres depends on the relative sense of the rings' circulation. Tracking the particles' motions makes possible measurements of the hydrodynamic coupling between the circular particle trains and addresses recently proposed hydrodynamic instabilities for collective colloidal motions on optical vortices.Comment: 7 pages, 2 figures, submitted to Europhysics Letter