Exact Results of the 1D 1/r21/r^2 Supersymmetric t-J Model without Translational Invariance

In this work, we continue the study of the supersymmetric t-J model with 1/r^2 hopping and exchange without translational invariance. A set of Jastrow wavefunctions are obtained for the system, with eigenenergies explicitly calculated. The ground state of the t-J model is included in this set of wavefunctions. The spectrum of this t-J model consists of equal-distant energy levels which are highly degenerate.Comment: 14 pages, Late

Mechanical Characterization and Shape Optimization of Fascicle-Like 3D Skeletal Muscle Tissues Contracted with Electrical and Optical Stimuli

Here we present a quantitative approach to constructing effective 3D muscle tissues through shape optimization and load impedance matching with electrical and optical stimulation. We have constructed long, thin, fascicle-like skeletal muscle tissue and optimized their form factor through mechanical characterization. A new apparatus was designed and built which allowed us to measure force-displacement characteristics with diverse load stiffnesses. We have found that a) there is an optimal form factor that maximizes the muscle stress, b) the energy transmitted to the load can be maximized with matched load stiffness, and c) optical stimulation using channelrhodopsin2 in the muscle tissue can generate twitch force as large as its electrical counterpart for well developed muscle tissue. Using our tissue construct method we found an optimal initial diameter of 500 microns outperformed tissues using 250 microns by more than 60% and tissues using 760 microns by 105%. Using an optimal load stiffness, our tissues have generated 12 pJ of energy at a peak generated stress of 1.28 kPa. Additionally, the difference in optically stimulated twitch performance vs. electrically stimulated is a function of how well the overall tissue performs, with average or better performing strips having less than 10% difference. The unique mechanical characterization method used is generalizable to diverse load conditions and will be used to match load impedance to muscle tissue impedance for a wide variety of applications.National Science Foundation (U.S.) (Grant No. CBET-0939511)Singapore-MIT Alliance for Research and Technology (BioSyM IRG)National Science Foundation (U.S.). Emergent Behaviors of Integrated Cellular System

Stochastic Modeling and Control of Biological Systems: The Lactose Regulation System of Escherichia Coli

In this paper, we present a comprehensive framework for stochastic modeling, model abstraction, and controller design for a biological system. The first half of the paper concerns modeling and model abstraction of the system. Most models in systems biology are deterministic models with ordinary differential equations in the concentration variables. We present a stochastic hybrid model of the lactose regulation system of E. coli bacteria that capture important phenomena which cannot be described by continuous deterministic models.We then show that the resulting stochastic hybrid model can be abstracted into a much simpler model, a two-state continuous-time Markov chain. The second half of the paper discusses controller design for a specific architecture. The architecture consists of measurement of a global quantity in a colony of bacteria as an output feedback and manipulation of global environmental variables as control actuation. We show that controller design can be performed on the abstracted (Markov chain) model and implementation on the real model yields the desired result

Investigation of pre‑treatment techniques to improve membrane performance in real textile wastewater treatment

Membrane technology has a significant role in textile wastewater treatment considering the modular design of the membrane processes that enables to conceive a complete treatment scheme. The study presents a comparative study of microfiltration (MF) (0.2 µm and 0.05 µm), ultrafiltration (UF), ozonation (0.1, 0.2 g/L ozone), ultraviolet (UV) irradiation and titanium dioxide (TiO2) (0.05, 0.15, 0.3, 0.5 g/L TiO2) and zeolite adsorption (125, 250, 500 mL/min flow rates) processes as pre-treatment prior to nanofiltration (NF) and reverse osmosis (RO) membranes for the treatment of real textile washing wastewater (WW). Experiments demonstrated that the applied pre-treatment methods enhanced the flux performance of NF270 and RO membranes except zeolite adsorption. By evaluation of all pre-treatment alternatives, it was seen that the best chemical oxygen demand (COD) removal efficiency (41%) was achieved with MF0.05 membrane. The highest conductivity removal efficiencies were obtained by UV/TiO2 application and with ozonation process the colour of the wastewater was removed at a performance of 80.5%, that was the highest among all pre-treatment applications. Based on the permeate flux and quality, the best pre-treatment method was selected as MF membrane with a pore size of 0.05 µm. Best conductivity removal efficiency was obtained by MF0.05 + XLE membrane combination at 93.6%. Also, considerably high COD removals were achieved with pre-treated NF and RO combinations together with a significant colour elimination (> 98%). In this study, it is aimed to create an efficient system that can be applied in real textile wastewater treatment by creating a combined treatment process

Harnessing bacterial power in microscale actuation

This paper presents a systematic analysis of the motion of microscale structures actuated by flagellated bacteria. We perform the study both experimentally and theoretically. We use a blotting procedure to attach flagellated bacteria to a buoyancy-neutral plate called a microbarge. The motion of the plate depends on the distribution of the cells on the plate and the stimuli from the environment. We construct a stochastic mathematical model for the system, based on the assumption that the behavior of each bacterium is random and independent of that of its neighbors. The main finding of the paper is that the motion of the barge plus bacteria system is a function of a very small set of parameters. This reduced-dimensional model can be easily estimated using experimental data. We show that the simulation results obtained from the model show an excellent match with the experimentally-observed motion of the barge

Formation and optogenetic control of engineered 3D skeletal muscle bioactuators

Densely arrayed skeletal myotubes are activated individually and as a group using precise optical stimulation with high spatiotemporal resolution. Skeletal muscle myoblasts are genetically encoded to express a light-activated cation channel, Channelrhodopsin-2, which allows for spatiotemporal coordination of a multitude of skeletal myotubes that contract in response to pulsed blue light. Furthermore, ensembles of mature, functional 3D muscle microtissues have been formed from the optogenetically encoded myoblasts using a high-throughput device. The device, called “skeletal muscle on a chip”, not only provides the myoblasts with controlled stress and constraints necessary for muscle alignment, fusion and maturation, but also facilitates the measurement of forces and characterization of the muscle tissue. We measured the specific static and dynamic stresses generated by the microtissues and characterized the morphology and alignment of the myotubes within the constructs. The device allows testing of the effect of a wide range of parameters (cell source, matrix composition, microtissue geometry, auxotonic load, growth factors and exercise) on the maturation, structure and function of the engineered muscle tissues in a combinatorial manner. Our studies integrate tools from optogenetics and microelectromechanical systems (MEMS) technology with skeletal muscle tissue engineering to open up opportunities to generate soft robots actuated by a multitude of spatiotemporally coordinated 3D skeletal muscle microtissues.National Science Foundation (U.S.) (Science and Technology Center—Emergent Behaviors of Integrated Cellular Systems (EBICS) grant No. CBET-0939511)National Institutes of Health (U.S.) (EB00262)National Science Foundation (U.S.) (GM74048)National Science Foundation (U.S.) (HL90747)National Institute for Biomedical Imaging and Bioengineering (U.S.) (RESBIO, Integrapted Technologies for Polymeric Biomaterial)University of Pennsylvania. Center for Engineering Cells and RegenerationSingapore-MIT Alliance for Research and Technolog

Metformin reduces airway glucose permeability and hyperglycaemia-induced Staphylococcus aureus load independently of effects on blood glucose

Background Diabetes is a risk factor for respiratory infection, and hyperglycaemia is associated with increased glucose in airway surface liquid and risk of Staphylococcus aureus infection. Objectives To investigate whether elevation of basolateral/blood glucose concentration promotes airway Staphylococcus aureus growth and whether pretreatment with the antidiabetic drug metformin affects this relationship. Methods Human airway epithelial cells grown at air–liquid interface (±18 h pre-treatment, 30 μM–1 mM metformin) were inoculated with 5×105 colony-forming units (CFU)/cm2 S aureus 8325-4 or JE2 or Pseudomonas aeruginosa PA01 on the apical surface and incubated for 7 h. Wild-type C57BL/6 or db/db (leptin receptor-deficient) mice, 6–10 weeks old, were treated with intraperitoneal phosphate-buffered saline or 40 mg/kg metformin for 2 days before intranasal inoculation with 1×107 CFU S aureus. Mice were culled 24 h after infection and bronchoalveolar lavage fluid collected. Results Apical S aureus growth increased with basolateral glucose concentration in an in vitro airway epithelia–bacteria co-culture model. S aureus reduced transepithelial electrical resistance (RT) and increased paracellular glucose flux. Metformin inhibited the glucose-induced growth of S aureus, increased RT and decreased glucose flux. Diabetic (db/db) mice infected with S aureus exhibited a higher bacterial load in their airways than control mice after 2 days and metformin treatment reversed this effect. Metformin did not decrease blood glucose but reduced paracellular flux across ex vivo murine tracheas. Conclusions Hyperglycaemia promotes respiratory S aureus infection, and metformin modifies glucose flux across the airway epithelium to limit hyperglycaemia-induced bacterial growth. Metformin might, therefore, be of additional benefit in the prevention and treatment of respiratory infection