bluuebunny/crossref_metadata_2025_split huggingface dataset:
Troisi\`eme groupe de cohomologie non ramifi\'ee des torseurs universels sur les surfaces rationnelles
Authors: Cao Yang 
Published: February 2021

Let $k$ a field of characteristic zero. Let $X$ be a smooth, projective, geometrically rational $k$-surface. Let $\mathcal{T}$ be a universal torsor over $X$ with a $k$-point et $\mathcal{T}^c$ a smooth compactification of $\mathcal{T}$. There is an open question: is $\mathcal{T}^c$ $k$-birationally equivalent to a projective space? We know that the unramified cohomology groups of degree 1 and 2 of $\mathcal{T}$ and $\mathcal{T}^c$ are reduced to their constant part. For the analogue of the third cohomology groups, we give a sufficient condition using the Galois structure of the geometrical Picard group of $X$. This enables us to show that $H^{3}_{nr}(\mathcal{T}^{c},\mathbb{Q}/\mathbb{Z}(2))/H^3(k,\mathbb{Q}/\mathbb{Z}(2))$ vanishes if $X$ is a generalised Ch\^atelet surface and that this group is reduced to its $2$-primary part if $X$ is a del Pezzo surface of degree at least 2.Comment: 27 page, in French
Hyper-K\"ahler Fourfolds Fibered by Elliptic Products
Authors: Kamenova Ljudmila 
Published: February 2021

Every fibration of a projective hyper-K\&quot;ahler fourfold has fibers which are Abelian surfaces. In case the Abelian surface is a Jacobian of a genus two curve, these have been classified by Markushevich. We study those cases where the Abelian surface is a product of two elliptic curves, under some mild genericity hypotheses.Comment: 8 pages, EPIGA published version
Limits of the trivial bundle on a curve
Authors: Beauville Arnaud 
Published: February 2021

We attempt to describe the rank 2 vector bundles on a curve C which are specializations of the trivial bundle. We get a complete classifications when C is Brill-Noether generic, or when it is hyperelliptic; in both cases all limit vector bundles are decomposable. We give examples of indecomposable limit bundles for some special curves.Comment: Final version, published in Epiga
$\overline{M}_{1,n}$ is usually not uniruled in characteristic $p$
Authors: Sawin Will 
Published: February 2021

Using etale cohomology, we define a birational invariant for varieties in characteristic $p$ that serves as an obstruction to uniruledness - a variant on an obstruction to unirationality due to Ekedahl. We apply this to $\overline{M}_{1,n}$ and show that $\overline{M}_{1,n}$ is not uniruled in characteristic $p$ as long as $n \geq p \geq 11$. To do this, we use Deligne's description of the etale cohomology of $\overline{M}_{1,n}$ and apply the theory of congruences between modular forms.Comment: 10 pages, published version
Equivariant perverse sheaves on Coxeter arrangements and buildings
Authors: Weissman Martin H. 
Published: February 2021

When $W$ is a finite Coxeter group acting by its reflection representation on $E$, we describe the category ${\mathsf{Perv}}_W(E_{\mathbb C}, {\mathcal{H}}_{\mathbb C})$ of $W$-equivariant perverse sheaves on $E_{\mathbb C}$, smooth with respect to the stratification by reflection hyperplanes. By using Kapranov and Schechtman's recent analysis of perverse sheaves on hyperplane arrangements, we find an equivalence of categories from ${\mathsf{Perv}}_W(E_{\mathbb C}, {\mathcal{H}}_{\mathbb C})$ to a category of finite-dimensional modules over an algebra given by explicit generators and relations. We also define categories of equivariant perverse sheaves on affine buildings, e.g., $G$-equivariant perverse sheaves on the Bruhat--Tits building of a $p$-adic group $G$. In this setting, we find that a construction of Schneider and Stuhler gives equivariant perverse sheaves associated to depth zero representations.Comment: 28 pages, 6 figures. v5 processed for publication in Epiga
CARTAN GEOMETRIES ON COMPLEX MANIFOLDS OF ALGEBRAIC DIMENSION ZERO
Authors: Biswas Indranil , Dumitrescu Sorin , Mckay Benjamin 
Published: February 2021

We show that compact complex manifolds of algebraic dimension zero bearing a holomorphic Cartan geometry of algebraic type have infinite fundamental group. This generalizes the main Theorem in [DM] where the same result was proved for the special cases of holomorphic affine connections and holomorphic conformal structures.Nous montrons que toute variété complexe compacte de dimension algébrique nulle possédant une géométrie de Cartan holomorphe de type algébrique doit avoir un groupe fondamental infini. Il s’agit d’une généralisation du théorème principal de [DM] où le même résultat était montré dans le cas particulier des connexions affines holomorphes et des structures conformes holomorphes.
Variation of stable birational types in positive characteristic
Authors: Schreieder Stefan 
Published: February 2021

Let k be an uncountable algebraically closed field and let Y be a smooth projective k-variety which does not admit a decomposition of the diagonal. We prove that Y is not stably birational to a very general hypersurface of any given degree and dimension. We use this to study the variation of the stable birational types of Fano hypersurfaces over fields of arbitrary characteristic. This had been initiated by Shinder, whose method works in characteristic zero.Comment: 14 pages; final version, published in EPIGA
Fujiki relations and fibrations of irreducible symplectic varieties
Authors: Schwald Martin 
Published: February 2021

This paper concerns different types of singular complex projective varieties generalizing irreducible symplectic manifolds. We deduce from known results that the generalized Beauville-Bogomolov form satisfies the Fujiki relations and has the same rank as in the smooth case. This enables us to study fibrations of these varieties; imposing the newer definition from [GKP16, Definition 8.16.2] we show that they behave much like irreducible symplectic manifolds.Comment: Published version
Opers of higher types, Quot-schemes and Frobenius instability loci
Authors: Joshi Kirti , Pauly Christian 
Published: February 2021

In this paper we continue our study of the Frobenius instability locus in the coarse moduli space of semi-stable vector bundles of rank $r$ and degree $0$ over a smooth projective curve defined over an algebraically closed field of characteristic $p&gt;0$. In a previous paper we identified the &quot;maximal&quot; Frobenius instability strata with opers (more precisely as opers of type $1$ in the terminology of the present paper) and related them to certain Quot-schemes of Frobenius direct images of line bundles. The main aim of this paper is to describe for any integer $q \geq 1$ a conjectural generalization of this correspondence between opers of type $q$ (which we introduce here) and Quot-schemes of Frobenius direct images of vector bundles of rank $q$. We also give a conjectural formula for the dimension of the Frobenius instability locus.Comment: 17 pages; Final version Epijournal de G'eom'etrie Alg'ebrique, Volume 4 (2020), Article Nr. 17
Rationally connected rational double covers of primitive Fano varieties
Authors: Pukhlikov Aleksandr V. 
Published: February 2021

We show that for a Zariski general hypersurface $V$ of degree $M+1$ in ${\mathbb P}^{M+1}$ for $M\geqslant 5$ there are no Galois rational covers $X\dashrightarrow V$ of degree $d\geqslant 2$ with an abelian Galois group, where $X$ is a rationally connected variety. In particular, there are no rational maps $X\dashrightarrow V$ of degree 2 with $X$ rationally connected. This fact is true for many other families of primitive Fano varieties as well and motivates a conjecture on absolute rigidity of primitive Fano varieties.Comment: the final journal version
Exceptional collections on certain Hassett spaces
Authors: Castravet Ana-Maria , Tevelev Jenia 
Published: February 2021

We construct an $S_2\times S_n$ invariant full exceptional collection on Hassett spaces of weighted stable rational curves with $n+2$ markings and weights $(\frac{1}{2}+\eta, \frac{1}{2}+\eta,\epsilon,\ldots,\epsilon)$, for $0&lt;\epsilon, \eta\ll1$ and can be identified with symmetric GIT quotients of $(\mathbb{P}^1)^n$ by the diagonal action of $\mathbb{G}_m$ when $n$ is odd, and their Kirwan desingularization when $n$ is even. The existence of such an exceptional collection is one of the needed ingredients in order to prove the existence of a full $S_n$-invariant exceptional collection on $\overline{\mathcal{M}}_{0,n}$. To prove exceptionality we use the method of windows in derived categories. To prove fullness we use previous work on the existence of invariant full exceptional collections on Losev-Manin spaces.Comment: At the request of the referee, the paper arXiv:1708.06340 has been split into two parts. This is the second of those papers (submitted). 36 pages
Motives with modulus, I: Modulus sheaves with transfers for non-proper modulus pairs
Authors: Kahn Bruno , Miyazaki Hiroyasu , Saito Shuji , Yamazaki Takao 
Published: February 2021

We develop a theory of modulus sheaves with transfers, which generalizes Voevodsky's theory of sheaves with transfers. This paper and its sequel are foundational for the theory of motives with modulus, which is developed in [KMSY20].Comment: 64 pages
An Ornamentalist View of Metaphor in Arabic Literary Theory
Authors: Shuqair Khaled M. 
Published: February 2021

The aim of the present paper is to examine the kind of thinking and the chain of assumptions that lie behind the reduction of metaphor to a mere ornament in Arabic literary theory. For this purpose, Arabic ornamentalist thinking is traced from the third century A.H. (the ninth century A.D.) to the seventh century A.H. (the thirteenth century A.D.). This is not to say, however, that the seventh century marks the end of such thinking in Arabic literary theory, but that at that time the Arabic literary theory, and the theory of metaphor, was developed into fixtures with an increasing emphasis given to form over content and the art of verbal expression in general. Inordinate attention was given to ornate style, and rhetoric became an arena for displaying verbal acrobatics. The axioms, "closeness of resemblance" and "congruity of metaphorical elements," represent metaphor's highest degree of formalization and stereotyping. That is why some of the images in classical theory are mainly based on complete parallelism between the objects compared, particularly with regard to form, size and color. From that time onwards, the fixtures of the classical theory have been kept intact. Metaphor, and rhetoric in general, is nowadays reduced to textbooks to be studied in abstract and rigid terms developed by the classical theory. Arabic rhetoric is a dead discipline: it is merely an ornamental repertoire of figures that could only be used as a sweet adorner for the language.
THE INFLUENCE OF PARENTAL DEMANDINGNESS ON MALE ADOLESCENT REBELLIOUS BEHAVIOUR IN PUBLIC SECONDARY SCHOOLS
Authors: Macharia Jane , Shikuku Dr. Mulambula M 
Published: February 2021

Purpose: The purpose of this study was to determine the influence of parental demandingness on male adolescent rebellious behaviour in public secondary schools in Kiambu district. Methodology: The study used ex-post facto research design. Stratified sampling was used to select the participants in the study. Schools were stratified into single sex and co-education schools. Systematic sampling using the class lists was used to identify the students who constituted the sample. The research instruments were the students’ questionnaire, the deputy principal’s and the teacher counsellor’s interview guide. The sample constituted 240 male students, six deputy principles and six teacher counselors. A pilot study was done to pre-test the research instruments so as to estimate their reliability and validity. Data collected was analyzed using Statistical Package for Social Sciences (SPSS). The findings were presented using descriptive and inferential statistics. Descriptive statistics included, frequency distribution, means, bar graphs, and tabulated according to the research objectives. Inferential statistics used included Chi Square and pearson correlation to test the hypotheses at 90% and 95% level of confidence; correlation coefficient was used to measure the strength of linear relationship between the variables of the study.Results: The results indicated that rebellious behaviour was positively and significantly correlated to parental demandingness.Unique contribution to theory, practice and policy: The study came up with a model that is recommended to schools for adoption by guidance and counselling teachers to help create awareness and understanding to both the students and parents with the aim of improving or bettering their relationship, academic performance and prevent rebellion in public secondary schools.
DETERMINANTS OF CAREER CHANGE AMONG TEACHERS IN RURAL KENYA: THE CASE OF TANA RIVER COUNTY
Authors: Kiongo Patrick 
Published: February 2021

Purpose: The purpose of this study was to investigate the determinants of career change in rural schools. The study was based on the theory of occupational choice and career typology theory. From the context of the theories, the underlying determinants under investigation were categorized into environmental, organizational and individual factors.Methodology: The study applied both inferential and descriptive survey research. Stratified and simple random sampling techniques were used to identify one hundred forty-seven (147) respondents from a study population of 1,555 teachers distributed in one hundred eighty-two public schools. The study used questionnaire as key instrument to acquire primary data while desk review of reports and publications was applied for secondary data.Findings: The study revealed that 55% of the respondents harbored plans to switch to other career later in life with individuality factors being the most significant compared to environmental and organizational factors which ranked second and third respectively.Unique Contribution to Practice and Policy: Educational institutions should therefore strive to achieve a sustainable balance between the teacher intrinsic and extrinsic influences in management of teacher career change. The findings of this study will illuminate policy assumptions behind different strategies used in efforts to alleviate problems associated with teacher’s career change in rural areas. In addition, the affected teachers will have a common understanding of challenges affecting them and have a common voice in articulating their issues for policy consideration.
Tecnologías digitales innovadoras para el diseño de exoesqueletos para la mano aplicados en la rehabilitación de pacientes con artritis crónica
Authors: Magal-Royo Teresa , Moya-Jiménez Roberto , Ponce Diana 
Published: February 2021

El artículo describe la metodología planteada en el diseño de creación de un prototipo de exoesqueleto para la rehabilitación de la artritis reumatoide enfermedad inflamatoria, sistémica y crónica que afecta principalmente al sistema osteomuscular de pies, manos y que desemboca a la larga, en una discapacidad funcional severa. La propuesta de diseño del exoesqueleto de la mano descrito en el artículo tiene en cuenta los accionamientos mecánicos aplicados sobre las articulaciones mediante el uso de servomotores conectados a hilos tensores que permiten el movimiento de flexo-extensión correcto de los dedos. Se propone un planteamiento sistémico en la creación del prototipo final considerando los parámetros de esfuerzos y movimientos que se utilizan normalmente en la rehabilitación convencional y la creación de un dispositivo generado con técnicas de prototipado rápido de la mano tratada que permita diseñar un exoesqueleto único y exacto basado en las características antropométricas de cada paciente. El resultado final ha permitido validar y verificar el proceso de desarrollo innovador de técnicas relacionadas con el Diseño Asistido por Ordenador, DAO y el Prototipado Rápido PR.
Sonographic measurements for spleen size in healthy Saudi children and correlation with body parameters
Authors: Mohtasib Rafat S. , Alshamiri Kamal , Jobeir Aman , Ambu-Saidi Farida Mohsin , Masawi Ahmed , Alabdulaziz Lamya , Hussain Faisal Bin 
Published: February 2021

BACKGROUND:
Ultrasound is commonly the first-line imaging modality for assessing the visceral organ dimensions without any risk of radiation. An abnormal size of the spleen may indicate disease, but the evaluation is challenging because of the normal size changes with age. In addition, published normal value charts for children may vary by population and methods.

OBJECTIVES:
Determine normal growth curves for splenic length in relationship to sex, age, body weight, height, body mass index, and body surface area of healthy children in Saudi Arabia.

DESIGN:
A retrospective review of ultrasonography images

SETTING:
Tertiary referral hospital

SUBJECTS AND METHODS:
We included all normal ultrasonography exams of splenic length (from full-term neonates to 16 years of age) performed between 2003 and 2018. The greatest longitudinal distance of the spleen from the dome to the tip (splenic length) measured at the hilum in the coronal plane was obtained by ultrasonography.

MAIN OUTCOME MEASURES:
The relationship between the longitudinal length of the spleen and sex, age, height, weight, body mass index, and body surface area.

SAMPLE SIZE:
1028 healthy children

RESULTS:

Height had the most significant correlation with the length of the spleen (
P
<.001). There was a consistent difference in splenic length according to sex. The spleen was longer in males than in females in children older than 2 years. In terms of splenic growth according to age, our data showed a statistically significant correlation between the ages of 0-24 months and 2-16 years. There was a significant difference between cases from Saudi Arabia, the United States (
P
=.023) and India (
P
=.045).

CONCLUSION:
We developed scatter plots between splenic lengths and body parameters among Saudi children for children from 0 day to 24 months and children from 2 years to 16 years for reference.

LIMITATION:
Retrospective study. Ultrasound techniques in patient positioning, and cursor placement differed from other studies, which can affect measurements of splenic length.

CONFLICTS OF INTEREST:
None.
The value of repeating fine-needle aspiration for thyroid nodules
Authors: Doubi Aseel , Alrayes Nuha S. , Alqubaisi Abdulaziz K. , Al-Dhahri Saleh F. 
Published: February 2021

BACKGROUND:
Fine-needle aspiration (FNA) is an invaluable technique used in the evaluation of thyroid nodules.

OBJECTIVES:
Evaluate the concordance of results for consecutive FNA readings.

DESIGN:
Retrospective, descriptive.

SETTINGS:
Two tertiary care centers.

METHODS:
Demographics were collected along with every FNA result and final pathology results for all patients (aged 9-90 years old) who underwent thyroid surgery from 2010 to 2017. The Bethesda system was used for cytology. Agreement levels were calculated and compared with final pathology.

SAMPLE SIZE:
Of 1237 initially included, 1134 had at least one FNA performed with results available for review.

RESULTS:
For the 1134 patients, demographic and clinical data were collection and a comparison was made between the three FNA results; the highest agreement was between FNA 2 and 3 (53.6%); however, the kappa value was consistently low for all comparisons, indicating a poor level of agreement overall. Also, the risk of malignancy was higher in this study than in the 2017 Bethesda system for reporting thyroid cytopathology in FNA cytology categories I and II.

CONCLUSION:
Repeating FNA biopsies yield different results every time; hence, there is a low level of agreement. The clinical decision should therefore include other important risk factors. Prospective studies could help shed more light on this topic.

LIMITATIONS:
Retrospective design.

CONFLICT OF INTEREST:
None.
La historia local y las construcciones conmemorativas
Authors: Ojeda Veloz Melba 
Published: February 2021

En el trabajo se exponen las principales consideraciones teóricas y metodológicas que fundamentan una Estrategia Pedagógica para el trabajo con las construcciones conmemorativas en el 2do ciclo de la enseñanza primaria. El objetivo se encamina a proponer formas no convencionales de enseñanza de la historia local, para lograr su vinculación con los contenidos de la historia nacional, teniendo en cuenta la importancia que ofrecen las fuentes históricas para la educación en valores y el fortalecimiento de la identidad nacional. Se utilizan métodos del nivel teórico y empírico que permiten definir las etapas de la misma y los principales resultados de su implementación en escolares del 2do ciclo de la enseñanza primaria.
La función del postgrado para el desarrollo local en el contexto del vínculo universidad-empresa
Authors: Concepción Toledo Diana N. 
Published: February 2021

Los Lineamientos de la Política Económica y Social del Partido y la Revolución (PCC, 2011), plantearon cambios radicales en la concepción del desarrollo económico y social territorial. De lo que se trata entonces, es de encontrar una solución y seguramente para muchos, en cualquier contexto, es realizar una eficiente gestión de Innovación para formular proyectos alternativos que puedan ser implementados con beneficios económicos, sociales y ambientales y energéticos, en la formulación de los cuales las universidades pueden impactar notablemente en el desarrollo local.En el presente artículo,se ha verificado como la actividad de postgrado es un aspecto clave para la solución directa de problemas específicos del desarrollo de un municipio en lo económico, social, energético y ambiental lo que se ejemplifica con la solución a 21 problemas específicos de un municipio logrados mediante la incorporación directa de especialistas de esa comunidad al trabajo científico bajo la dirección de especialistas altamente preparados de dos universidades vinculadas al territorio.
El proyecto técnico en la solución de problemas profesionales
Authors: Torres Ferrales Alberto Luis , Montano Moreno Geordanis , Martínez Pérez Alejandro Ermes 
Published: February 2021

El presente trabajo tiene como objetivo proponer una variante del método de proyectos para la solución de problemas técnicos. Se introduce la utilización del método análisis de objetos técnicos y se eliminan etapas de método de proyecto tradicional. Se utilizaron diferentes métodos para la corroborar la factibilidad de la propuesta, dentro de ellos el criterio de usuarios y el criterio de expertos.
Enseñar a solucionar problemas profesionales a los futuros profesionales es una necesidad en el proceso formativo. Estos problemas se manifiestan en las esferas de la producción y los servicios donde se insertará el profesional una vez egresados de las instituciones formadoras. Los problemas profesionales se manifiestan a través de situaciones profesionales. Con frecuencia la situación profesional se origina a partir de un problema técnico cuya solución depende de la aplicación del método de proyecto. La aplicación de esta variante ha permitido determinar los problemas profesionales que enfrenta el profesional en su esfera de actuación, ya sea en la producción o en los servicios y solucionar los problemas técnicos que se manifiestan en los referidos problemas.
L' immagine di Federico II di Svevia
Authors: Vagnoni Mirko 
Published: February 2021

La critica storiografica ha spesso visto, forse un po’ troppo entusiasticamente, la rappresentazione dell’imperatore Federico II di Svevia in una cospicua serie di manufatti artistici. Passando in rassegna presunte e reali raffigurazioni dello Svevo nella sfragistica, nella numismatica, nella glittica, nell’oreficeria, nella scultura, nella pittura e nella miniatura, in questo saggio si fa lo Status quaestionis sulla ritrattistica fridericiana cercando di delineare quali furono le immagini prodotte all’interno della sua corte e su sua stessa iniziativa, in altre parole le sue raffigurazioni ufficiali. Giungeremo così, dopo un percorso ad esclusione che lascerà ben pochi superstiti, a rintracciare quei ritratti che lo Stupor mundi volle dare di sé e che ancora oggi sono conservati.