599 research outputs found
Mechanical signatures of microbial biofilms in micropillar-embedded growth chambers
Biofilms are surface-attached communities of microorganisms embedded in an extracellular matrix and are essential for the cycling of organic matter in natural and engineered environments. They are also the leading cause of many infections, for example, those associated with chronic wounds and implanted medical devices. The extracellular matrix is a key biofilm component that determines its architecture and defines its physical properties. Herein, we used growth chambers embedded with micropillars to study the net mechanical forces (differential pressure) exerted during biofilm formation in situ. Pressure from the biofilm is transferred to the micropillars via the extracellular matrix, and reduction of major matrix components decreases the magnitude of micropillar deflections. The spatial arrangement of micropillar deflections caused by pressure differences in the different biofilm strains may potentially be used as mechanical signatures for biofilm characterization. Hence, we submit that micropillar-embedded growth chambers provide insights into the mechanical properties and dynamics of the biofilm and its matrix.Singapore. National Research Foundation (Singapore-MIT Alliance for Research and Technology (SMART)
Generalization of the Luttinger Theorem for Fermionic Ladder Systems
We apply a generalized version of the Lieb-Schultz-Mattis Theorem to
fermionic ladder systems to show the existence of a low-lying excited state
(except for some special fillings). This can be regarded as a non-perturbative
proof for the conservation under interaction of the sum of the Fermi wave
vectors of the individual channels, corresponding to a generalized version of
the Luttinger Theorem to fermionic ladder systems. We conclude by noticing that
the Lieb-Schultz-Mattis Theorem is not applicable in this form to show the
existence of low-lying excitations in the limit that the number of legs goes to
infinity, e.g. in the limit of a 2D plane.Comment: RevTex, 4 pages with 4 eps figure
Vascular pedicle width in acute lung injury: correlation with intravascular pressures and ability to discriminate fluid status
Abstract Introduction Conservative fluid management in patients with acute lung injury (ALI) increases time alive and free from mechanical ventilation. Vascular pedicle width (VPW) is a non-invasive measurement of intravascular volume status. The VPW was studied in ALI patients to determine the correlation between VPW and intravascular pressure measurements and whether VPW could predict fluid status. Methods This retrospective cohort study involved 152 patients with ALI enrolled in the Fluid and Catheter Treatment Trial (FACTT) from five NHLBI ARDS (Acute Respiratory Distress Syndrome) Network sites. VPW and central venous pressure (CVP) or pulmonary artery occlusion pressure (PAOP) from the first four study days were correlated. The relationships between VPW, positive end-expiratory pressure (PEEP), cumulative fluid balance, and PAOP were also evaluated. Receiver operator characteristic (ROC) curves were used to determine the ability of VPW to detect PAOP <8 mmHg and PAOP â„18 mm Hg. Results A total of 71 and 152 patients provided 118 and 276 paired VPW/PAOP and VPW/CVP measurements, respectively. VPW correlated with PAOP (r = 0.41; P < 0.001) and less well with CVP (r = 0.21; P = 0.001). In linear regression, VPW correlated with PAOP 1.5-fold better than cumulative fluid balance and 2.5-fold better than PEEP. VPW discriminated achievement of PAOP <8 mm Hg (AUC = 0.73; P = 0.04) with VPW â€67 mm demonstrating 71% sensitivity (95% CI 30 to 95%) and 68% specificity (95% CI 59 to 75%). For discriminating a hydrostatic component of the edema (that is, PAOP â„18 mm Hg), VPW â„72 mm demonstrated 61.4% sensitivity (95% CI 47 to 74%) and 61% specificity (49 to 71%) (area under the curve (AUC) 0.69; P = 0.001). Conclusions VPW correlates with PAOP better than CVP in patients with ALI. Due to its only moderate sensitivity and specificity, the ability of VPW to discriminate fluid status in patients with acute lung injury is limited and should only be considered when intravascular pressures are unavailable
From high temperature supercondutivity to quantum spin liquid: progress in strong correlation physics
This review gives a rather general discussion of high temperature
superconductors as an example of a strongly correlated material. The argument
is made that in view of the many examples of unconventional superconductors
discovered in the past twenty years, we should no longer be surprised that
superconductivity emerges as a highly competitive ground state in systems where
Coulomb repulsion plays a dominant role. The physics of the cuprates is
discussed, emphasizing the unusual pseudogap phase in the underdoped region. It
is argued that the resonating valence bond (RVB) picture, as formulated using
gauge theory with fermionic and bosonic matter fields, gives an adequate
physical understanding, even though many details are beyond the powers of
current calculational tools. The recent discovery of quantum oscillations in a
high magnetic field is discussed in this context. Meanwhile, the problem of the
quantum spin liquid (a spin system with antiferromagnetic coupling which
refuses to order even at zero temperature) is a somewhat simpler version of the
high problem where significant progress has been made recently. It is
understood that the existence of matter fields can lead to de-confinement of
the U(1) gauge theory in 2+1 dimensions, and novel new particles (called
fractionalized particles), such as fermionic spinons which carry spin and no charge, and gapless gauge bosons can emerge to create a new critical
state at low energies. We even have a couple of real materials where such a
scenario may be realized experimentally. The article ends with answers to
questions such as: what limits if pairing is driven by an electronic
energy scale? why is the high problem hard? why is there no consensus?
and why is the high problem important?Comment: Submitted as "Key Issue" essay for Report of Progress in Physics; v2:
References are added and typos correcte
An open label pilot trial of lowâdose lithium for young people at ultraâhigh risk for psychosis
Aim: Lithium, even at low doses, appears to offer neuroprotection against a wide variety of insults. In this controlled pilot, we examined the safety (i.e., sideâeffect profile) of lithium in a sample of young people identified at ultraâhigh risk (UHR) for psychosis. The secondary aim was to explore whether lithium provided a signal of clinical efficacy in reducing transition to psychosis compared with treatment as usual (TAU). Methods: Young people attending the PACE clinic at Orygen, Melbourne, were prescribed a fixed dose (450 mg) of lithium (n = 25) or received TAU (n = 78). The primary outcome examined sideâeffects, with transition to psychosis, functioning and measures of psychopathology assessed as secondary outcomes. Results: Participants in both groups were functionally compromised (lithium group GAF = 56.6; monitoring group GAF = 56.9). Sideâeffect assessment indicated that lithium was wellâtolerated. 64% (n = 16) of participants in the lithium group were lithiumâadherent to week 12. Few cases transitioned to psychosis across the study period; lithium group 4% (n = 1); monitoring group 7.7% (n = 6). There was no difference in time to transition to psychosis between the groups. No group differences were observed in other functioning and symptom domains, although all outcomes improved over time. Conclusions: With a sideâeffect profile either comparable to, or better than UHR antipsychotic trials, lithium might be explored for further research with UHR young people. A definitive larger trial is needed to determine the efficacy of lithium in this cohort
An SU(2) Formulation of the t-J model: Application to Underdoped Cuprates
We develop a slave-boson theory for the t-J model at finite doping which
respect a SU(2) symmetry -- a symmetry previously known to be important at half
filling. The mean field phase diagram is found to be consistent with the phases
observed in the cuprate superconductors, which contains d-wave superconductor,
spin gap, strange metal, and Fermi liquid phases. The spin gap phase is best
understood as the staggered flux phase, which is nevertheless translationally
invariant for physical quantities. The physical electron spectral function
shows small Fermi segments at low doping which continuously evolve into the
large Fermi surface at high doping concentrations. The close relation between
the SU(2) and the U(1) slave-boson theory is discussed. The low energy
effective theory for the low lying fluctuations is derived, and new lying modes
(which were over looked in the U(1) theory) are identified.Comment: 28 pages, 8 figures, RevTe
Chemical shark repellent: Myth or fact? The effect of a shark necromone on shark feeding behaviour
a b s t r a c t Since 1942, the search for an effective chemical shark repellent has been ongoing research concern in the United States. A long-standing anecdote that sharks avoid areas containing decomposing shark tissue has initiated new interest in identifying trace chemical alarm signals produced during decomposition (necromones). A commercially-sourced shark necromone produced from putrefied shark tissue was evaluated over a five-year period in South Bimini, Bahamas. Competitively-feeding populations of Caribbean reef sharks (Carcharhinus perezi) and blacknose sharks (Carcharhinus acronotus) were exposed to necromones using pressurized aerosol canisters at the surface. Shark density estimations were made at the initial, 1 min and 5 min intervals after preliminary exposure along with continuous exposure of feeding stimulus. In both species, an unambiguous halt in feeding behavior was observed within 1 min after exposure of the necromone. For aerosol delivery, a 150 mL dose of the necromone from a single aerosol canister is able to halt all feeding activity in a combined population of C. perezi and C. acronotus. Shark necromones induced a spectacular alarm response in interacting sharks resulting in a temporary evacuation of an area containing feeding stimuli. Additionally, sharks were not deterred by alternative treatment presentations of 10% weight percent (w/w) aqueous urea, 10% w/w oleic acid in ethanol, or water buffered to pH 8.5. Habituation to the necromone was not observed for repeated tests at the same location. In all experiments, the presence of a shark necromone did not produce a similar aversion response for teleosts as observed in C. perezi or C. acronotus; however, anecdotal observations demonstrate that teleosts increased their feeding rate in the presence of the necromone. Experimental controls using denatured ethanol or water confirmed that feeding sharks were not deterred by bubbles, sound, or the solvents used to extract the necromones. Comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry indicates that the necromone is a complex solution rich in amino acids and putrefaction products. Experiments demonstrate that the key chemical component responsible for the alarm response is within these amino acids and/or putrefaction products, but further experimentation is needed to more accurately identify the active ingredient. Shark necromones hold particular promise for use in shark bycatch reduction and conservation. The existence of a putative chemical shark repellent has been confirmed
Online and social networking interventions for the treatment of depression in young people: a systematic review
BACKGROUND: Major depression accounts for the greatest burden of all diseases globally. The peak onset of depression occurs between adolescence and young adulthood, and for many individuals, depression displays a relapse-remitting and increasingly severe course. Given this, the development of cost-effective, acceptable, and population-focused interventions for depression is critical. A number of online interventions (both prevention and acute phase) have been tested in young people with promising results. As these interventions differ in content, clinician input, and modality, it is important to identify key features (or unhelpful functions) associated with treatment outcomes. OBJECTIVE: A systematic review of the research literature was undertaken. The review was designed to focus on two aspects of online intervention: (1) standard approaches evaluating online intervention content in randomized controlled designs (Section 1), and (2) second-generation online interventions and services using social networking (eg, social networking sites and online support groups) in any type of research design (Section 2). METHODS: Two specific literature searches were undertaken. There was no date range specified. The Section 1 search, which focused on randomized controlled trials, included only young people (12-25 years) and yielded 101 study abstracts, of which 15 met the review inclusion criteria. The Section 2 search, which included all study design types and was not restricted in terms of age, yielded 358 abstracts, of which 22 studies met the inclusion criteria. Information about the studies and their findings were extracted and tabulated for review. RESULTS: The 15 studies identified in Section 1 described 10 trials testing eight different online interventions, all of which were based on a cognitive behavioral framework. All but one of the eight identified studies reported positive results; however, only five of the 15 studies used blinded interviewer administered outcomes with most trials using self-report data. Studies varied significantly in presentation of intervention content, treatment dose, and dropout. Only two studies included moderator or clinician input. Results for Section 2 were less consistent. None of the Section 2 studies reported controlled or randomized designs. With the exception of four studies, all included participants were younger than 25 years of age. Eight of the 16 social networking studies reported positive results for depression-related outcomes. The remaining studies were either mixed or negative. Findings for online support groups tended to be more positive; however, noteworthy risks were identified. CONCLUSIONS: Online interventions with a broad cognitive behavioral focus appear to be promising in reducing depression symptomology in young people. Further research is required into the effectiveness of online interventions delivering cognitive behavioral subcomponents, such as problem-solving therapy. Evidence for the use of social networking is less compelling, although limited by a lack of well-designed studies and social networking interventions. A range of future social networking therapeutic opportunities are highlighted
MIPModDB: a central resource for the superfamily of major intrinsic proteins
The channel proteins belonging to the major intrinsic proteins (MIP) superfamily are diverse and are found in all forms of life. Water-transporting aquaporin and glycerol-specific aquaglyceroporin are the prototype members of the MIP superfamily. MIPs have also been shown to transport other neutral molecules and gases across the membrane. They have internal homology and possess conserved sequence motifs. By analyzing a large number of publicly available genome sequences, we have identified more than 1000 MIPs from diverse organisms. We have developed a database MIPModDB which will be a unified resource for all MIPs. For each MIP entry, this database contains information about the source, gene structure, sequence features, substitutions in the conserved NPA motifs, structural model, the residues forming the selectivity filter and channel radius profile. For selected set of MIPs, it is possible to derive structure-based sequence alignment and evolutionary relationship. Sequences and structures of selected MIPs can be downloaded from MIPModDB database which is freely available at http://bioinfo.iitk.ac.in/MIPModDB
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