Quantum Tricritical Points in NbFe2_2

Quantum critical points (QCPs) emerge when a 2nd order phase transition is suppressed to zero temperature. In metals the quantum fluctuations at such a QCP can give rise to new phases including unconventional superconductivity. Whereas antiferromagnetic QCPs have been studied in considerable detail ferromagnetic (FM) QCPs are much harder to access. In almost all metals FM QCPs are avoided through either a change to 1st order transitions or through an intervening spin-density-wave (SDW) phase. Here, we study the prototype of the second case, NbFe$_2$. We demonstrate that the phase diagram can be modelled using a two-order-parameter theory in which the putative FM QCP is buried within a SDW phase. We establish the presence of quantum tricritical points (QTCPs) at which both the uniform and finite $q$ susceptibility diverge. The universal nature of our model suggests that such QTCPs arise naturally from the interplay between SDW and FM order and exist generally near a buried FM QCP of this type. Our results promote NbFe$_2$ as the first example of a QTCP, which has been proposed as a key concept in a range of narrow-band metals, including the prominent heavy-fermion compound YbRh$_2$Si$_2$.Comment: 21 pages including S

Towards polarization-based excitation tailoring for extended Raman spectroscopy

Undoubtedly, Raman spectroscopy is one of the most elaborate spectroscopy tools in materials science, chemistry, medicine and optics. However, when it comes to the analysis of nanostructured specimens or individual sub-wavelength-sized systems, the access to Raman spectra resulting from different excitation schemes is usually very limited. For instance, the excitation with an electric field component oriented perpendicularly to the substrate plane is a difficult task. Conventionally, this can only be achieved by mechanically tilting the sample or by sophisticated sample preparation. Here, we propose a novel experimental method based on the utilization of polarization tailored light for Raman spectroscopy of individual nanostructures. As a proof of principle, we create three-dimensional electromagnetic field distributions at the nanoscale using tightly focused cylindrical vector beams impinging normally onto the specimen, hence keeping the traditional beam-path of commercial Raman systems. In order to demonstrate the convenience of this excitation scheme, we use a sub-wavelength diameter gallium-nitride nanostructure as a test platform and show experimentally that its Raman spectra depend sensitively on its location relative to the focal vector field. The observed Raman spectra can be attributed to the interaction with transverse and pure longitudinal electric field components. This novel technique may pave the way towards a characterization of Raman active nanosystems, granting direct access to growth-related parameters such as strain or defects in the material by using the full information of all Raman modes

A Cross-Evaluated Database of Measured and Simulated HRTFs Including 3D Head Meshes, Anthropometric Features, and Headphone Impulse Responses

The individualization of head related transfer functions (HRTFs) can make an important contribution to improving the quality of binaural technology applications. One approach to individualization is to exploit the relationship between the shape of HRTFs and the anthropometric features of the ears, head, and torso of the corresponding listeners. To identify statistically significant relationships between the two sets of variables, a relatively large database is required. For this purpose full-spherical HRTFs of 96 subjects were acoustically measured and numerically simulated. A detailed cross-evaluation showed a good agreement to previous data between repeated measurements and between measured and simulated data. In addition to 96 HRTFs, the database includes high-resolution head-meshes, a list of 25 anthropometric features per subject, and headphone transfer functions for two headphone models

Perceptually Motivated Analysis of Numerically Simulated Head-Related Transfer Functions Generated By Various 3D Surface Scanning Systems

Numerical simulations offer a feasible alternative to the direct acoustic measurement of individual head-related transfer functions (HRTFs). For the acquisition of high quality 3D surface scans, as required for these simulations, several approaches exist. In this paper, we systematically analyze the variations between different approaches and evaluate the influence of the accuracy of 3D scans on the resulting simulated HRTFs. To assess this effect, HRTFs were numerically simulated based on 3D scans of the head and pinna of the FABIAN dummy head generated with 6 different methods. These HRTFs were analyzed in terms of interaural time difference, interaural level difference, energetic error in auditory filters and by their modeled localization performance. From the results, it is found that a geometric precision of about 1 mm is needed to maintain accurate localization cues, while a precision of about 4 mm is sufficient to maintain the overall spectral shape

The HUTUBS head-related transfer function (HRTF) database

The database contains head-related transfer functions, 3D head meshes, anthropometric features, and headphone transfer functions of 96 subjects

Quantum tricritical points in NbFe2

Quantum critical points (QCPs) emerge when a 2nd order phase transition is suppressed to zero temperature. In metals the quantum fluctuations at such a QCP can give rise to new phases including unconventional superconductivity. Whereas antiferromagnetic QCPs have been studied in considerable detail ferromagnetic (FM) QCPs are much harder to access. In almost all metals FM QCPs are avoided through either a change to 1st order transitions or through an intervening spin-density-wave (SDW) phase. Here, we study the prototype of the second case, NbFe$_2$. We demonstrate that the phase diagram can be modelled using a two-order-parameter theory in which the putative FM QCP is buried within a SDW phase. We establish the presence of quantum tricritical points (QTCPs) at which both the uniform and finite $q$ susceptibility diverge. The universal nature of our model suggests that such QTCPs arise naturally from the interplay between SDW and FM order and exist generally near a buried FM QCP of this type. Our results promote NbFe$_2$ as the first example of a QTCP, which has been proposed as a key concept in a range of narrow-band metals, including the prominent heavy-fermion compound YbRh$_2$Si$_2$

A decadal view of biodiversity informatics: challenges and priorities

Biodiversity informatics plays a central enabling role in the research community's efforts to address scientific conservation and sustainability issues. Great strides have been made in the past decade establishing a framework for sharing data, where taxonomy and systematics has been perceived as the most prominent discipline involved. To some extent this is inevitable, given the use of species names as the pivot around which information is organised. To address the urgent questions around conservation, land-use, environmental change, sustainability, food security and ecosystem services that are facing Governments worldwide, we need to understand how the ecosystem works. So, we need a systems approach to understanding biodiversity that moves significantly beyond taxonomy and species observations. Such an approach needs to look at the whole system to address species interactions, both with their environment and with other species. It is clear that some barriers to progress are sociological, basically persuading people to use the technological solutions that are already available. This is best addressed by developing more effective systems that deliver immediate benefit to the user, hiding the majority of the technology behind simple user interfaces. An infrastructure should be a space in which activities take place and, as such, should be effectively invisible. This community consultation paper positions the role of biodiversity informatics, for the next decade, presenting the actions needed to link the various biodiversity infrastructures invisibly and to facilitate understanding that can support both business and policy-makers. The community considers the goal in biodiversity informatics to be full integration of the biodiversity research community, including citizens’ science, through a commonly-shared, sustainable e-infrastructure across all sub-disciplines that reliably serves science and society alike

Dependability of direct behavior ratings across rater and occasion in students with externalizing behavior problems

Die vorliegende Studie untersucht die Zuverlässigkeit von Verhaltensverlaufsdiagnostik mittels Direct Behavior Rating (DBR) über Rater und Messzeitpunkte bei Schülern mit externalisierenden Verhaltensproblemen. Im Rahmen einer vollständig gekreuzten Zwei-Facetten-Generalisierbarkeitsstudie wurde das Verhalten von fünf Viertklässlern mit externalisierendem Problemverhalten (Facette Schüler) von einer Regelschullehrerin, sowie einer Lehrerin für sonderpädagogische Förderung (Facette Rater) zu insgesamt acht Unterrichtssituationen à zehn Minuten (Facette Messzeitpunkt) jeweils mit einer Single-Item-Skala (SIS) und einer Multi-Item-Skala (MIS) beurteilt. Die Ergebnisse weisen auf einen starken Einfluss der Messzeitpunkte auf die Zuverlässigkeit der Messung sowohl bei den SIS als auch bei den MIS hin. Die Facette Rater klärt hingegen nur bei den SIS einen substanziellen Anteil der Gesamtvarianz auf. Die Ergebnisse einer Simulationsstudie über eine unterschiedliche Anzahl an Messzeitpunkten zeigen, dass zuverlässige Ergebnisse zur Interpretation intraindividueller Verhaltensverläufe nur mittels MIS in einem überschaubaren Zeitraum (13 Messzeitpunkte) erzielt werden. Die Ergebnisse ermutigen für den praktischen Einsatz der Methode zur Evaluation des Erfolgs einer Verhaltensfördermaßnahme. (DIPF/Orig.)The purpose of the current study was the analysis of the reliability of Direct Behavior Ratings (DBR) across raters and occasions for students with externalizing problem behaviors. A fully-crossed Generalizability study design was conducted, wherein one female regular classroom teacher as well as one female special education teacher (facet rater) rated the externalizing problem behavior of five male fourth-graders (facet students) in eight instructional phases of independent seatwork (facet occasion) with a single item scale (SIS) and a multi item scale (MIS). The results indicate a strong influence of the time-related factor (occasion) on the reliability of both SIS and MIS. The facet rater contributes a substantial part of the total variance for the SIS. Results of a decision study across a different number of occasions yield dependable results for interpreting intra-individual behavior progress for the MIS after 13 occasions. The results strengthen the practical use of DBR to collect progress monitoring data in order to evaluate a students’ individuals response to an intervention. (DIPF/Orig.

Generalizability and dependability of direct behavior ratings of academically engaged behavior in an inclusive classroom setting

Die vorliegende Studie untersucht die Generalisierbarkeit und Zuverlässigkeit von Direkten Verhaltensbeurteilungen (DVB) des Lern- und Arbeitsverhaltens in einer inklusiven Grundschule. In einer Generalisierbarkeitsstudie mit einem vollständig gekreuzten Zwei-Facetten-Design (Rater und Item) werden 10 Grundschulkinder von 6 geschulten Beurteilenden anhand von gefilmten Unterrichtsphasen beobachtet und das Lern- und Arbeitsverhalten mit einer DVB mit 5 Items eingeschätzt. Die Ergebnisse der Generalisierbarkeitsstudie zeigen erwartungskonform eine hohe Varianzaufklärung durch Unterschiede zwischen den Personen. Allerdings ist der Interaktionseffekt zwischen Ratern und Kindern trotz umfangreicher Schulung substantiell. Dennoch weisen die Ergebnisse einer Entscheidungsstudie auf eine hohe Generalisierbarkeit und Zuverlässigkeit der Daten hin. Die Befunde sprechen für einen Einsatz des Instruments zur Verlaufsdiagnostik von Schülerverhalten. (DIPF/Orig.)This study focuses on generalizability and dependability of direct behavior ratings of academically engaged behavior in an inclusive classroom setting. In a fully-crossed 2 facet generalizability study design (raters and items) 6 trained observers rated 10 students’ academically engaged behavior with a direct behavior rating multiple item scale. As expected, results of the generalizability study show that differences between persons explain most of the total variance. However, the interaction between raters and students is despite rater training relatively high. Nevertheless, decision study results suggest good generalizability and dependability. The results support the usability of direct behavior ratings for formative assessment of student behavior. (DIPF/Orig.