959 research outputs found
Upconversion nanoparticles for sensing pH.
Upconversion nanoparticles (UCNPs) can provide a vehicle for chemical imaging by coupling chemically sensitive dyes and quenchers. The mechanism for coupling of two anthraquinone dyes, Calcium Red and Alizarin Red S, was investigated as a function of pH. The green emission band of the UCNPs was quenched by a pH-dependent inner filter effect (IFE) while the red emission band remained unchanged and acted as the reference signal for ratiometric pH measurements. Contrary to previous expectation, there was little evidence for a resonance energy transfer (RET) mechanism even when the anthraquinones were attached onto the UCNPs through electrostatic attraction. Since the UCNPs are point emitters, only emitters close to the surface of the UCNP are within the expected Förster distance and UC-RET is <10%. The theoretical and experimental analysis of the interaction between UCNPs and pH-sensitive quenchers will allow the design of UCNP pH sensors for determination of pH via IFE.This work was supported by the EPSRC Cambridge NanoDTC, EP/L015978/
The hazards of lack of co-registration of ictal brain SPECT with MRI: A case report of sinusitis mimicking a brainstem seizure focus
BACKGROUND: Single photon emission computed tomography (SPECT) following injection of radiotracer during a seizure is known as ictal SPECT. Comparison of an ictal SPECT study to a baseline or interictal study can aid identification of a seizure focus. CASE PRESENTATION: A young woman with encephalitis and refractory seizures underwent brain SPECT during a period of frequent seizure-like episodes, and during a seizure-free period. A focal area of increased radiotracer uptake present only when she was experiencing frequent seizure-like episodes was originally localized to the brainstem, but with later computerized co-registration of SPECT to MRI, was found to lie outside the brain, in the region of the sphenoid sinus. CONCLUSION: Low-resolution SPECT images present difficulties in interpretation, which can be overcome through co-registration to higher-resolution structural images
Absence of a Spin Liquid Phase in the Hubbard Model on the Honeycomb Lattice
A spin liquid is a novel quantum state of matter with no conventional order
parameter where a finite charge gap exists even though the band theory would
predict metallic behavior. Finding a stable spin liquid in two or higher
spatial dimensions is one of the most challenging and debated issues in
condensed matter physics. Very recently, it has been reported that a model of
graphene, i.e., the Hubbard model on the honeycomb lattice, can show a spin
liquid ground state in a wide region of the phase diagram, between a semi-metal
(SM) and an antiferromagnetic insulator (AFMI). Here, by performing numerically
exact quantum Monte Carlo simulations, we extend the previous study to much
larger clusters (containing up to 2592 sites), and find, if any, a very weak
evidence of this spin liquid region. Instead, our calculations strongly
indicate a direct and continuous quantum phase transition between SM and AFMI.Comment: 15 pages with 7 figures and 9 tables including supplementary
information, accepted for publication in Scientific Report
Criticality in correlated quantum matter
At quantum critical points (QCP)
\cite{Pfeuty:1971,Young:1975,Hertz:1976,Chakravarty:1989,Millis:1993,Chubukov:1
994,Coleman:2005} there are quantum fluctuations on all length scales, from
microscopic to macroscopic lengths, which, remarkably, can be observed at
finite temperatures, the regime to which all experiments are necessarily
confined. A fundamental question is how high in temperature can the effects of
quantum criticality persist? That is, can physical observables be described in
terms of universal scaling functions originating from the QCPs? Here we answer
these questions by examining exact solutions of models of correlated systems
and find that the temperature can be surprisingly high. As a powerful
illustration of quantum criticality, we predict that the zero temperature
superfluid density, , and the transition temperature, , of
the cuprates are related by , where the exponent
is different at the two edges of the superconducting dome, signifying the
respective QCPs. This relationship can be tested in high quality crystals.Comment: Final accepted version not including minor stylistic correction
Obstetric anal sphincter injury: a systematic review of information available on the internet.
OBJECTIVE: There is no systematic evaluation of online health information pertaining to obstetric anal sphincter injury. Therefore, we evaluated the accuracy, credibility, reliability, and readability of online information concerning obstetric anal sphincter injury. MATERIALS AND METHODS: Multiple search engines were searched. The first 30 webpages were identified for each keyword and considered eligible if they provided information regarding obstetric anal sphincter injury. Eligible webpages were assessed by two independent researchers for accuracy (prioritised criteria based upon the RCOG Third and Fourth Degree Tear guideline); credibility; reliability; and readability. RESULTS: Fifty-eight webpages were included. Seventeen webpages (30%) had obtained Health On the Net certification, or Information Standard approval and performed better than those without such approvals (p = 0.039). The best overall performing website was http://www.pat.nhs.uk (score of 146.7). A single webpage (1%) fulfilled the entire criteria for accuracy with a score of 18: www.tamesidehospital.nhs.uk . Twenty-nine webpages (50%) were assessed as credible (scores ≥7). A single webpage achieved a maximum credibility score of 10: www.meht.nhs.uk . Over a third (21 out of 58) were rated as poor or very poor. The highest scoring webpage was http://www.royalsurrey.nhs.uk (score 62). No webpage met the recommended Flesch Reading Ease Score above 70. The intra-class coefficient between researchers was 0.98 (95% CI 0.96-0.99) and 0.94 (95% CI 0.89-0.96) for accuracy and reliability assessments. CONCLUSION: Online information concerning obstetric anal sphincter injury often uses language that is inappropriate for a lay audience and lacks sufficient accuracy, credibility, and reliability
On the (anisotropic) uniform metallic ground states of fermions interacting through arbitrary two-body potentials in d dimensions
We demonstrate that the skeleton of the Fermi surface S_{F;s} pertaining to a
uniform metallic ground state (corresponding to fermions with spin index s) is
determined by the Hartree-Fock contribution to the dynamic self-energy. The
Fermi surface S_{F;s} consists of all points which in addition to satisfying
the quasi-particle equation in terms of the Hartree-Fock self-energy, fulfill
the equation S_{s}(k) = 0, where S_{s}(k) is defined in the main text; the set
of k points which satisfy the Hartree-Fock quasi-particle equation but fail to
satisfy S_{s}(k) = 0, constitute the pseudo-gap region of the putative Fermi
surface of the interacting system. We consider the behaviour of the
ground-state momentum-distribution function n_{s}(k) for k in the vicinity of
S_{F;s} and show that whereas for the uniform metallic ground states of the
conventional Hubbard Hamiltonian n_{s}(k) is greater/less than 0.5 for k
approaching S_{F;s} from inside/outside the Fermi sea, for interactions of
non-zero range these inequalities can be violated (without thereby contravening
the condition of the non-negativity of the possible jump in n_{s}(k) on k
crossing S_{F;s} from directly inside to directly outside the Fermi sea). We
discuss, in the light of the findings of the present work, the growing
experimental evidence with regard to the `frustration' of the kinetic energy of
the charge carriers in the normal states of the copper-oxide-based
high-temperature superconducting compounds. [Short abstract]Comment: 30 pages, 3 postscript figures. Brought into conformity with the
published versio
SPAM detection: Naïve bayesian classification and RPN expression-based LGP approaches compared
An investigation is performed of a machine learning algorithm and the Bayesian classifier in the spam-filtering context. The paper shows the advantage of the use of Reverse Polish Notation (RPN) expressions with feature extraction compared to the traditional Naïve Bayesian classifier used for spam detection assuming the same features. The performance of the two is investigated using a public corpus and a recent private spam collection, concluding that the system based on RPN LGP (Linear Genetic Programming) gave better results compared to two popularly used open source Bayesian spam filters. © Springer International Publishing Switzerland 2016
Cost-Effectiveness of Genotypic Antiretroviral Resistance Testing in HIV-Infected Patients with Treatment Failure
BACKGROUND: Genotypic antiretroviral resistance testing (GRT) in HIV infection with drug resistant virus is recommended to optimize antiretroviral therapy, in particular in patients with virological failure. We estimated the clinical effect, cost and cost-effectiveness of using GRT as compared to expert opinion in patients with antiretroviral treatment failure. METHODS: We developed a mathematical model of HIV disease to describe disease progression in HIV-infected patients with treatment failure and compared the incremental impact of GRT versus expert opinion to guide antiretroviral therapy. The analysis was conducted from the health care (discount rate 4%) and societal (discount rate 2%) perspective. Outcome measures included life-expectancy, quality-adjusted life-expectancy, health care costs, productivity costs and cost-effectiveness in US Dollars per quality-adjusted life-year (QALY) gained. Clinical and economic data were extracted from the large Swiss HIV Cohort Study and clinical trials. RESULTS: Patients whose treatment was optimized with GRT versus expert opinion had an increase in discounted life-expectancy and quality-adjusted life-expectancy of three and two weeks, respectively. Health care costs with and without GRT were US 419,000, leading to an incremental cost-effectiveness ratio of US 551,000 and $US 549,000, respectively. When productivity changes were included in the analysis, GRT was cost-saving. CONCLUSIONS: GRT for treatment optimization in HIV-infected patients with treatment failure is a cost-effective use of scarce health care resources and beneficial to the society at large
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