Thermal Ising transitions in the vicinity of two-dimensional quantum critical points

The scaling of the transition temperature into an ordered phase close to a quantum critical point as well as the order parameter fluctuations inside the quantum critical region provide valuable information about universal properties of the underlying quantum critical point. Here, we employ quantum Monte Carlo simulations to examine these relations in detail for two-dimensional quantum systems that exhibit a finite-temperature Ising-transition line in the vicinity of a quantum critical point that belongs to the universality class of either (i) the three-dimensional Ising model for the case of the quantum Ising model in a transverse magnetic field on the square lattice or (ii) the ${\it chiral}$ Ising transition for the case of a half-filled system of spinless fermions on the honeycomb lattice with nearest-neighbor repulsion. While the first case allows large-scale simulations to assess the scaling predictions to a high precision in terms of the known values for the critical exponents at the quantum critical point, for the later case we extract values of the critical exponents $\nu$ and $\eta$, related to the order parameter fluctuations, which we discuss in relation to other recent estimates from ground state quantum Monte Carlo calculations as well as analytical approaches.Comment: 11 pages, 13 figure

Bond-ordered states and ff-wave pairing of spinless fermions on the honeycomb lattice

Spinless fermions on the honeycomb lattice with repulsive nearest-neighbor interactions are known to harbour a quantum critical point at half-filling, with critical behaviour in the Gross-Neveu (chiral Ising) universality class. The critical interaction strength separates a weak-coupling semimetallic regime from a commensurate charge-density-wave phase. The phase diagram of this basic model of correlated fermions on the honeycomb lattice beyond half-filling is, however, less well established. Here, we perform an analysis of its many-body instabilities using the functional renormalization group method with a basic Fermi surface patching scheme, which allows us to treat instabilities in competing channels on equal footing also away from half-filling. Between half-filling and the van-Hove filling, the free Fermi surface is hole-like and we again find a charge-density wave instability to be dominant at large interactions. Moreover, its characteristics are those of the half-filled case. Directly at the van-Hove filling the nesting property of the free Fermi surface stabilizes a dimerized bond-order phase. At lower filling the free Fermi surface becomes electron-like and a superconducting instability with $f$-wave symmetry is found to emerge from the interplay of intra-unitcell repulsion and collective fluctuations in the proximity to the charge-density wave instability. We estimate the extent of the various phases and extract the corresponding order parameters from the effective low-energy Hamiltonians.Comment: 11 pages, 11 figure

Priming in a shape task but not in a category task under continuous flash suppression

Continuous flash suppression (CFS) is an interocular suppression technique that uses high-contrast masks flashed to one eye to prevent conscious perception of images shown to the other eye. It has become widely used due to its strength and prolonged duration of suppression and its nearly deterministic control of suppression onset and offset. Recently, it has been proposed that action-relevant visual processing ascribed to the dorsal stream remains functional, while processing in the ventral stream is completely suppressed, when stimuli are invisible under CFS. Here we tested the hypothesis that the potentially dorsal-stream-based analysis of prime-stimulus elongation during CFS affects the categorization of manipulable target objects. In two behavioral experiments, we found evidence for priming in a shape task, but none for priming in a category task, when prime stimuli were rendered invisible using CFS. Our results thus support the notion that the representation of CF-suppressed stimuli is more limited than previously thought

Training improves visual processing speed and generalizes to untrained functions

Studies show that manipulating certain training features in perceptual learning determines the specificity of the improvement. The improvement in abnormal visual processing following training and its generalization to visual acuity, as measured on static clinical charts, can be explained by improved sensitivity or processing speed. Crowding, the inability to recognize objects in a clutter, fundamentally limits conscious visual perception. Although it was largely considered absent in the fovea, earlier studies report foveal crowding upon very brief exposures or following spatial manipulations. Here we used GlassesOff's application for iDevices to train foveal vision of young participants. The training was performed at reading distance based on contrast detection tasks under different spatial and temporal constraints using Gabor patches aimed at testing improvement of processing speed. We found several significant improvements in spatio-temporal visual functions including near and also non-trained far distances. A remarkable transfer to visual acuity measured under crowded conditions resulted in reduced processing time of 81 ms, in order to achieve 6/6 acuity. Despite a subtle change in contrast sensitivity, a robust increase in processing speed was found. Thus, enhanced processing speed may lead to overcoming foveal crowding and might be the enabling factor for generalization to other visual functions

Clinical value of a combined multi-phase contrast enhanced DOPA-PET/CT in neuroendocrine tumours with emphasis on the diagnostic CT component

Objective: To assess the clinical value of multi-phase, contrast-enhanced DOPA-PET/CT with emphasis on the diagnostic CT component in patients with neuroendocrine tumours (NET). Methods: Sixty-five patients with NET underwent DOPA-cePET/CT. The DOPA-PET, multi-phase CT and combined DOPA cePET/CT data were evaluated and diagnostic accuracies compared. The value of ceCT in DOPA cePET/CT concerning lesion detection and therapeutic impact was evaluated. Sensitivities, specificities and accuracies were calculated. Histopathology and clinical follow-up served as the standard of reference. Differences were tested for statistical significance by McNemar's test. Results: In 40 patients metastatic and/or primary tumour lesions were detected. Lesion-based analysis for the DOPA-PET showed sensitivity, specificity and accuracy of 66%, 100% and 67%, for the ceCT data 85%, 71% and 85%, and for the combined DOPA cePET/CT data 97%, 71% and 96%. DOPA cePET/CT was significantly more accurate compared with dual-phase CT (p < 0.05) and PET alone (p < 0.05). Additional lesion detection was based on ceCT in 12 patients; three patients underwent significant therapeutic changes based on the ceCT findings. Conclusion: DOPA cePET/CT was significantly more accurate than DOPA-PET alone and ceCT alone. The CT component itself had a diagnostic impact in a small percentage but contributed to the therapeutic strategies in selected patient

Therapeutic impact of [18F]fluoride positron-emission tomography/computed tomography on patients with unclear foot pain

Purpose: To evaluate the therapeutic impact of [18F]fluoride positron-emission tomography/computed tomography ([18F]fluoride PET/CT) imaging on patients with unclear foot pain. Methods: Twenty-eight patients were prospectively included in this study. Therapeutic management was defined by two experienced dedicated foot surgeons before and after [18F]fluoride PET/CT imaging. Twenty-six patients underwent cross-sectional imaging [CT, magnetic resonance (MR)] prior to PET/CT. A retrospective analysis of the magnetic resonance imaging (MRI) diagnoses was performed when a therapy change occurred after PET/CT imaging. Results: In 13/28 (46%) patients therapeutic management was changed due to PET/CT results. Management changes occurred in patients with the following diagnoses: os trigonum syndrome; sinus tarsi syndrome; os tibiale externum syndrome; osteoarthritis of several joints; non-consolidated fragments; calcaneo-navicular coalition; plantar fasciitis; insertional tendinopathy; suggestion of periostitis; neoarticulations between metatarsal bones. Os trigonum, os tibiale externum, subtalar osteoarthritis and plantar fasciitis were only seen to be active on PET/CT images but not on MR images. Conclusion: [18F]fluoride PET/CT has a substantial therapeutic impact on management in patients with unclear foot pai

A Tale of Two Academic Communities: Digital Imaginaries of Automatic Screening Tools in Editorial Practice

Automatic screening tools such as plagiarism scanners play an increasing role in journals’ efforts to detect and prevent violations of research integrity. More than just neutral technological means, these tools constitute normatively charged instruments for governance. Employing the analytical concept of the digital imaginary, this contribution investigates the normative concepts that play a role in journals’ use of automatic screening. Using survey data of journal editors, as well as guidance documents by academic publishers and the Committee of Publication Ethics, it traces how editors normatively situate their (non-)use of automatic screening tools in two opposing imaginaries of academic publishing: One that portrays academic publishing as a small and safe community, and one that sees it as a vast and dangerous space. These imaginaries reflect the social and epistemic characteristics and publication cultures in different academic fields, and both entail different modes of control. Additionally, they are shaped by a focus on plagiarism screening as a specific form of automatic screening that critically hinges on the issue of size of the publishing space, which exemplifies the mutual constitution of a specific problem, an imaginary where this problem becomes meaningful, and the availability of a tool that targets this problem.Peer Reviewe

18F-Fluoride PET/CT for detection of sacroiliitis in ankylosing spondylitis

Purpose: The aim of this study was to evaluate the performance of 18F-fluoride-PET/CT (PET/CT) for the diagnosis of sacroiliac joint (SIJ) arthritis in patients with active ankylosing spondylitis (AS). Methods: Included in the study were 15 patients with AS according to the modified New York criteria (AS group) and with active disease and 13 patients with mechanical low back pain (MLBP; control group) who were investigated with whole-body 18F-fluoride PET/CT. The ratio of the uptake in the SIJ and that in the sacrum (SIJ/S) was calculated for every joint. Results: The mean SIJ/S ratio of 30 quantified joints in the AS group was 1.66 (range 1.10-3.07) with PET/CT, and the mean SIJ/S ratio of 26 quantified joints in the MLBP group was 1.12 (range 0.71-1.52). The area under the receiver operating characteristic curve for SIJ arthritis was 0.84. With plain radiography as a the gold standard and taking an SIJ/S ratio of >1.3 as the threshold, the sensitivity, specificity and accuracy on a per patient basis were 80%, 77% and 79%, respectively. On a per SIJ basis, the greatest sensitivity (94%) was found in grade 3 sacroiliitis (n = 16). Conclusion: Our results suggest that quantitative 18F-fluoride PET/CT may play a role in the diagnosis of sacroiliitis in active AS and is an alternative to conventional bone scintigraphy in times of molybdenum shortag

Assessment of successful incorporation of cages after cervical or lumbar intercorporal fusion with [(18)F]fluoride positron-emission tomography/computed tomography

The purpose of this study is to assess the successful incorporation of cages in patients after cervical or lumbar intercorporal fusion with positron-emission tomography/computed tomography (PET/CT). Twenty patients (14 female and 6 male; mean age 58years, age range 38-73years) with 30 cervical (n=13) or lumbar (n=17) intercorporal fusions were prospectively enrolled in this study. Time interval between last intercorporal intervention and PET/CT ranged from 2 to 116months (mean 63; median 77months). IRB approval was obtained for all patients, and written informed consent was obtained from all patients. About 30min prior to PET/CT scanning, 97-217MBq (mean 161MBq) 18F-fluoride were administered intravenously. Patients were imaged in supine position on a combined PET/CT system (Discovery RX/STE, 16/64 slice CT, GE Healthcare). 3D-PET emission data were acquired for 1.5 and 2min/bed position, respectively, and reconstructed by a fully 3D iterative algorithm (VUE Point HD) using low-dose CT data for attenuation correction. A dedicated diagnostic thin-slice CT was optionally acquired covering the fused region. Areas of increased 18F-fluoride uptake around cages were determined by one double-board certified radiologist/nuclear physician and one board certified radiologist in consensus. In 12/20 (60%) patients, increased 18F-fluoride uptake around cages was observed. Of the 30 intercorporal fusions, 15 (50%) showed increased 18F-fluoride uptake. Median time between intervention and PET/CT examination in cages with increased uptake was 37months (2-116months), median time between intervention and PET/CT examination in those cages without increased uptake was 91months (19-112months), p (Wilcoxon)=0.01 (one-sided). 14/29 (48%) cages with a time interval>1year between intervention and PET/CT scan showed an increased uptake. In conclusion, PET/CT frequently shows increased 18F-fluoride uptake in cervical and lumbar cages older than 1year (up to almost 8years in cervical cages and 10years in lumbar cages) possibly indicating unsuccessful fusion due to increased stress/microinstabilit