Microtubule buckling in an elastic matrix with quenched disorder

The intracellular elastic matrix has been recognized as an important factor to stabilize microtubules and increase their critical buckling force in vivo. This phenomenon was qualitatively explained by the Winkler model, which investigated buckling of a filament embedded in a homogeneous elastic medium. However, the assumption of homogeneity of the matrix in Winkler's, and other advanced models, is unrealistic inside cells, where the local environment is highly variable along the filament. Considering this to be a quenched-disorder system, we use a Poisson distribution for confinements, and apply the replica technique combined with the Gaussian variational method to address the buckling of a long filament. The results show two types of filament buckling: one corresponding to the first-order, and the other to a continuous second-order phase transition. The critical point, i.e. the switch from first- to second-order buckling transition, is induced by the increase in disorder strength. We also discover that this random disorder of the elastic environment destabilizes the filament by decreasing $P_c$ from the Winkler result, and the matrix with stronger mean elasticity has a stronger role of disorder (inhomogeneity). For microtubules in vivo, buckling follows the discontinuous first-order transition, with the threshold reduced to the fraction between 0.9 and 0.75 of the Winkler prediction for the homogeneous elastic matrix. We also show that disorder can affect the force-displacement relationship at non-zero temperature, while at zero temperature this effect vanishes.This work has been supported by the Theory of Condensed Matter Critical Mass Grant from EPSRC (EP/J017639)

Stiffening of under-constrained spring networks under isotropic strain

Disordered spring networks are a useful paradigm to examine macroscopic mechanical properties of amorphous materials. Here, we study the elastic behavior of under-constrained spring networks, i.e.\ networks with more degrees of freedom than springs. While such networks are usually floppy, they can be rigidified by applying external strain. Recently, an analytical formalism has been developed to predict the mechanical network properties close to this rigidity transition. Here we numerically show that these predictions apply to many different classes of spring networks, including phantom triangular, Delaunay, Voronoi, and honeycomb networks. The analytical predictions further imply that the shear modulus $G$ scales linearly with isotropic stress $T$ close to the rigidity transition; however, this seems to be at odds with recent numerical studies suggesting an exponent between $G$ and $T$ that is smaller than one for some network classes. Using increased numerical precision and shear stabilization, we demonstrate here that close to the transition linear scaling, $G\sim T$, holds independent of the network class. Finally, we show that our results are not or only weakly affected by finite-size effects, depending on the network class.Comment: 17 pages, 10 figure

Infection Control Preparedness for Human Infection With Influenza A H7N9 in Hong Kong

Objective. To assess the effectiveness of infection control preparedness for human infection with influenza A H7N9 in Hong Kong Design. A descriptive study of responses to the emergence of influenza A H7N9 Setting. A university-affiliated teaching hospital Participants. Healthcare workers (HCWs) with unprotected exposure (not wearing N95 respirator during aerosol-generating procedure) to a patient with influenza A H7N9 Methods. A bundle approach including active and enhanced surveillance, early airborne infection isolation, rapid molecular diagnostic testing, and extensive contact tracing for HCWs with unprotected exposure was implemented. Seventy HCWs with unprotected exposure to an index case were interviewed especially regarding their patient care activities Results. From April 1, 2013, through May 31, 2014, a total of 126 (0.08%) of 163,456 admitted patients were tested for the H7 gene by reverse transcription-polymerase chain reaction per protocol. Two confirmed cases were identified. Seventy (53.8%) of 130 HCWs had unprotected exposure to an index case, whereas 41 (58.6%) and 58 (82.9%) of 70 HCWs wore surgical masks and practiced hand hygiene after patient care, respectively. Sixteen (22.9%) of 70 HCWs were involved in high-risk patient contacts. More HCWs with high-risk patient contacts received oseltamivir prophylaxis (P= 0.088) and significantly more had paired sera collected for H7 antibody testing (P<0.001). Ten (14.3%) of 70 HCWs developed influenza-like illness during medical surveillance, but none had positive results by reverse transcriptionpolymerase chain reaction. Paired sera was available from 33 of 70 HCWs with unprotected exposure, and none showed seroconversion against H7N9 Conclusions. Despite the delay in airborne precautions implementation, no patient-to-HCW transmission of influenza A H7N9 was demonstrated. © 2015 by The Society for Healthcare Epidemiology of America. All rights reserved.published_or_final_versio

Hard-wall entropic effect accelerates detachment of adsorbed polymer chains.

Many previous studies of unbinding kinetics have focused on a two-state model, with fully bonded and free states, which may not extend to more complicated biopolymer dynamics involving other reactions. Here we address the kinetic rate of this process at the segment level, as it is influenced by a growing dangling end of the chain. We use the mean first-passage time approach and treat the polymer as a chain attached to a wall through a succession of spring potentials, with two distinct regions of bonded and free segments. The interaction between the wall and free-moving chain end adds an entropic repulsion to this process. We estimate the average monomer detachment rate K as a function of the free dangling length L. For a flexible polymer, we find an acceleration factor in the average detachment rate depending on L and the details of the spring bond; when L is long, this factor is a simple ratio of its breaking distance to the natural bond length. For a semiflexible filament, we examine the regime where L is shorter than persistence length L_{p}, as the limit opposite to that of the flexible chain. An enhancing factor also appears, speeding up the filament unbinding when the free length grows; for a long rigid rod, this factor becomes two, independently of the bond details. We also examine the total unbinding time of an irreversible detaching process by integrating (1/K) over polymer length and discover that its power-law scaling with chain length is smaller than one, over the commonly seen range of polymer size.This work is funded by the Theory of Condensed Matter Critical Mass Grant from EPSRC (EP/J017639)

An Algorithm for Preferential Selection of Spectroscopic Targets in LEGUE

We describe a general target selection algorithm that is applicable to any survey in which the number of available candidates is much larger than the number of objects to be observed. This routine aims to achieve a balance between a smoothly-varying, well-understood selection function and the desire to preferentially select certain types of targets. Some target-selection examples are shown that illustrate different possibilities of emphasis functions. Although it is generally applicable, the algorithm was developed specifically for the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) survey that will be carried out using the Chinese Guo Shou Jing Telescope. In particular, this algorithm was designed for the portion of LEGUE targeting the Galactic halo, in which we attempt to balance a variety of science goals that require stars at fainter magnitudes than can be completely sampled by LAMOST. This algorithm has been implemented for the halo portion of the LAMOST pilot survey, which began in October 2011.Comment: 17 pages, 7 figures, accepted for publication in RA

Hypermethylation of the TGF-β target, ABCA1 is associated with poor prognosis in ovarian cancer patients

Background The dysregulation of transforming growth factor-β (TGF-β) signaling plays a crucial role in ovarian carcinogenesis and in maintaining cancer stem cell properties. Classified as a member of the ATP-binding cassette (ABC) family, ABCA1 was previously identified by methylated DNA immunoprecipitation microarray (mDIP-Chip) to be methylated in ovarian cancer cell lines, A2780 and CP70. By microarray, it was also found to be upregulated in immortalized ovarian surface epithelial (IOSE) cells following TGF-β treatment. Thus, we hypothesized that ABCA1 may be involved in ovarian cancer and its initiation. Results We first compared the expression level of ABCA1 in IOSE cells and a panel of ovarian cancer cell lines and found that ABCA1 was expressed in HeyC2, SKOV3, MCP3, and MCP2 ovarian cancer cell lines but downregulated in A2780 and CP70 ovarian cancer cell lines. The reduced expression of ABCA1 in A2780 and CP70 cells was associated with promoter hypermethylation, as demonstrated by bisulfite pyro-sequencing. We also found that knockdown of ABCA1 increased the cholesterol level and promoted cell growth in vitro and in vivo. Further analysis of ABCA1 methylation in 76 ovarian cancer patient samples demonstrated that patients with higher ABCA1 methylation are associated with high stage (P = 0.0131) and grade (P = 0.0137). Kaplan-Meier analysis also found that patients with higher levels of methylation of ABCA1 have shorter overall survival (P = 0.019). Furthermore, tissue microarray using 55 ovarian cancer patient samples revealed that patients with a lower level of ABCA1 expression are associated with shorter progress-free survival (P = 0.038). Conclusions ABCA1 may be a tumor suppressor and is hypermethylated in a subset of ovarian cancer patients. Hypermethylation of ABCA1 is associated with poor prognosis in these patients

Stem cell membrane engineering for cell rolling using peptide conjugation and tuning of cell–selectin interaction kinetics

Dynamic cell–microenvironment interactions regulate many biological events and play a critical role in tissue regeneration. Cell homing to targeted tissues requires well balanced interactions between cells and adhesion molecules on blood vessel walls. However, many stem cells lack affinity with adhesion molecules. It is challenging and clinically important to engineer these stem cells to modulate their dynamic interactions with blood vessels. In this study, a new chemical strategy was developed to engineer cell–microenvironment interactions. This method allowed the conjugation of peptides onto stem cell membranes without affecting cell viability, proliferation or multipotency. Mesenchymal stem cells (MSCs) engineered in this manner showed controlled firm adhesion and rolling on E-selectin under physiological shear stresses. For the first time, these biomechanical responses were achieved by tuning the binding kinetics of the peptide-selectin interaction. Rolling of engineered MSCs on E-selectin is mediated by a Ca[superscript 2+] independent interaction, a mechanism that differs from the Ca[superscript 2+] dependent physiological process. This further illustrates the ability of this approach to manipulate cell–microenvironment interactions, in particular for the application of delivering cells to targeted tissues. It also provides a new platform to engineer cells with multiple functionalities.National Heart, Lung, and Blood Institute (Programs of Excellence in Nanotechnology Award Contract HHSN268201000045C)National Institutes of Health (U.S.) (Grant 2-P30-CA14051)Armed Forces Institute of Regenerative Medicine (Award W81XWH-08-2-0034

Examining the Factors Influencing Consumers’ Purchasing Intention for Genetically Modified Agricultural Food

The application of genetic engineering to food is becoming popular worldwide, especially in UK and USA. However, consumers in Asia remain unsure of the risks and benefits of genetically modified food. To measure the purchase intentions of Taiwanese and Vietnamese consumers using an integrated framework of the attitude model and the behavioral intention model, quantitative research was conducted in which the questionnaires were distributed to respondents living in Taiwan and in Vietnam. The results showed that the dependent variable of consumer attitude was positively impacted by three in-dependent variables including perceived risk to health, perceived benefit to health, and perceived benefit to the environment. The other construct showed no significant effect on consumers’ attitudes in the two countries. The consistency result in both countries between subjective norm and attitude revealed a positive impact on the purchase intention in descending order, while the variable of perceived behavioral control did not contribute to affecting purchase intention significantly. Finally, limitations and suggestions for future studies are also proposed