cometadata/datacite-rtg-text-other-reclassification-records huggingface dataset:
Views of middle school girls on calculator use in mathematics classes
Creators: name: Yu, Wendy
Publisher: name: University of British Columbia
Year: 2009

description: This study examined middle school students' perceptions of calculator use in the classroom. Through autobiographies and group interviews, the students expressed what they thought about how calculators are used and how they should be used. Calculators have been a topic of interest for many years now but with the advent of the modern computer, the calculator debate has been pushed to the sidelines. However, the question of how calculators should be used is constantly disputed. Some people believe calculators prevent the learning of the basics while others feel that calculators help students probe deeper into problems. This study addresses these concerns from the eyes of eight grade 8 students in middle school and attempts to answer the question: What do middle school students say about how calculators are used and should be used? The findings were based on individual opinion and experiences of students within the study. In summary, the majority of students gave positive feedback towards the use of calculators within the math class. However, there were some concerns regarding basic skills (such as addition, subtraction, multiplication and division) that were voiced as well. The students favoured calculator use as a tool in the math class as long as there was already a firm grasp of basic skills. Irrefutably, more time and a greater understanding of calculators by teachers will help students make the choice to use this tool effectively.
Testing for Oligopoly Power in the Kenyan Seed Maize Processing Industry
Creators: name: Nzuma, Jonathan M.
name: Nzuma, Jonathan M.
Publisher: name: Unknown
Year: 2006
Subjects: subject: Crop Production/Industries
subject: Industrial Organization
subject: Seed Maize
subject: Market power
subject: Lerner index
subject: Oligopoly

description: In the recent past, the concentration of seed maize processing and marketing in Kenya has raised serious public concerns. The inability of this industry to ensure affordable prices of certified seed maize for the farming community has led policy makers to question its market behaviour. In spite of these concerns, the performance of agricultural markets in Kenya has received little attention. This study evaluates the market conduct of the industry using the New Empirical Institutional Organization framework and tests the hypothesis of price taking behaviour. A system of five equations was used to estimate conjectural variations elasticity while a Lerner index was constructed to measure market power using data from Kenya's Central Bureau of Statistics. The estimated average conjectural variations elasticity of 0.702 was significantly different from zero and therefore the hypothesis of price taking was rejected. The degree of market power as measured by the difference between price and marginal cost was estimated at 0.450. In general, the estimated own price demand relationships conformed to economic theory except in the case of labour and capital where unexpected positive own price relationships were reported. The estimated conjectural elasticity and Lerner index indicated that the sector was anticompetitive in the period under analysis. These findings give compelling evidence to conclude that the assumption of price-taking behaviour is inappropriate for the seed maize processing industry in Kenya.
Low-cost precursor of an interstellar mission
Creators: name: Heller, René
name: Anglada-Escudé, Guillem
name: Hippke, Michael
name: Kervella, Pierre
Publisher: name: arXiv
Year: 2020
Subjects: subject: Instrumentation and Methods for Astrophysics (astro-ph.IM)
subject: Space Physics (physics.space-ph)
subject: FOS: Physical sciences

description: The solar photon pressure provides a viable source of thrust for spacecraft in the solar system. Theoretically it could also enable interstellar missions, but an extremely small mass per cross section area is required to overcome the solar gravity. We identify aerographite, a synthetic carbon-based foam with a density of 0.18 kg/m^3 (15,000 times more lightweight than aluminum) as a versatile material for highly efficient propulsion with sunlight. A hollow aerographite sphere with a shell thickness eps_shl = 1 mm could go interstellar upon submission to the solar radiation in interplanetary space. Upon launch at 1 AU from the Sun, an aerographite shell with eps_shl = 0.5 mm arrives at the orbit of Mars in 60 d and at Pluto's orbit in 4.3 yr. Release of an aerographite hollow sphere, whose shell is 1 micrometer thick, at 0.04 AU (the closest approach of the Parker Solar Probe) results in an escape speed of nearly 6900 km/s and 185 yr of travel to the distance of our nearest star, Proxima Centauri. The infrared signature of a meter-sized aerographite sail could be observed with JWST up to 2 AU from the Sun, beyond the orbit of Mars. An aerographite hollow sphere with eps_shl = 100 micrometer and a radius of 1 m (5 m) weighs 230 mg (5.7 g) and has a 2.2 g (55 g) mass margin for interstellar escape. The payload margin is ten times the mass of the spacecraft, whereas the payload on chemical interstellar rockets is typically a thousandth of the weight of the rocket. Simplistic communication would enable studies of the interplanetary medium and a search for the suspected Planet Nine, and would serve as a precursor mission to alpha Centauri. We estimate prototype developments costs of 1 million USD, a price of 1000 USD per sail, and a total of <10 million USD including launch for a piggyback concept with an interplanetary mission.
description: accepted in A&A, 13 pages, 9 Figures (6 col, 3 b/w), 1 Table
Microscopic Theory of Spontaneous Decay in a Dielectric
Creators: name: Fu, Hao
name: Berman, P. R.
Publisher: name: arXiv
Year: 2005
Subjects: subject: Quantum Physics (quant-ph)
subject: Other Condensed Matter (cond-mat.other)
subject: FOS: Physical sciences

description: The local field correction to the spontanous dacay rate of an impurity source atom imbedded in a disordered dielectric is calculated to second order in the dielectric density. The result is found to differ from predictions associated with both "virtual" and "real" cavity models of this decay process. However, if the contributions from two dielectric atoms at the same position are included, the virtual cavity result is reproduced.
description: 12 Pages
Magnetism and its coexistence with superconductivity in CaK(Fe$_{0.949}$Ni$_{0.051}$)$_4$As$_4$: muon spin rotation/relaxation studies
Creators: name: Khasanov, Rustem
name: Simutis, Gediminas
name: Pashkevich, Yurii G.
name: Shevtsova, Tatyana
name: Meier, William R.
name: Bud'ko, Sergey L.
name: Kogan, Vladimir G.
name: Canfield, Paul C.
Publisher: name: arXiv
Year: 2020
Subjects: subject: Superconductivity (cond-mat.supr-con)
subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: FOS: Physical sciences

description: The magnetic response of CaK(Fe$_{0.949}$Ni$_{0.051}$)$_4$As$_4$ was investigated by means of the muon-spin rotation/relaxation. The long-range commensurate magnetic order sets in below the Néel temperature $T_{\rm N}= 50.0(5)$~K. The density-functional theory calculations have identified three possible muon stopping sites. The experimental data were found to be consistent with only one type of magnetic structure, namely, the long-range magnetic spin-vortex-crystal order with the hedgehog motif within the $ab-$plane and the antiferromagnetic stacking along the $c-$direction. The value of the ordered magnetic moment at $T\approx3$ K was estimated to be $m_{\rm Fe}=0.38(11)$ $μ_{\rm B}$ ($μ_{\rm B}$ is the Bohr magneton). A microscopic coexistence of magnetic and superconducting phases accompanied by a reduction of the magnetic order parameter below the superconducting transition temperature $T_{\rm c}\simeq 9$ K is observed. Comparison with 11, 122, and 1144 families of Fe-based pnictides points to existence of correlation between the reduction of the magnetic order parameter at $T\rightarrow 0$ and the ratio of the transition temperatures $T_{\rm c}/T_{\rm N}$. Such correlations were found to be described by Machida's model for coexistence of itinerant spin-density wave magnetism and superconductivity [Machida, J. Phys. Soc. Jpn. 50, 2195 (1981) and Bud'ko et al., Phys. Rev. B 98, 144520 (2018)].
description: 15 pages, 14 figures
Improving the Performance of Retail Food Store Cashiers Through Better Training
Creators: name: Kriesberg, Martin
name: Kriesberg, Martin
Publisher: name: Unknown
Year: 1953
Subjects: Labor and Human Capital
Research Methods/ Statistical Methods

description: Excerpt from the report Summary: The performance of retail food store employees may be improved considerably more by instruction methods which emphasize employee participation than by methods which rely mainly on written memoranda. In a controlled experiment conducted among food store cashiers. The training method which gave cashiers an opportunity to participate in a group training conference and to help develop new procedures resulted in superior performance. Better performance was shown by more willing acceptance of new checkout procedures, closer adherence to established procedures, more courtesy to customers, better utilization of time, and more employee satisfaction with the instruction received. The experiment was conducted not only to learn whether each of these practices would be improved by the special training, but also to measure the degree of improvement over that obtained by written memoranda.
Automated computation of spin- and colour-correlated Born matrix elements
Creators: name: Weinzierl, Stefan
Publisher: name: arXiv
Year: 2005
Subjects: subject: High Energy Physics - Phenomenology (hep-ph)
subject: FOS: Physical sciences

description: I report on an implementation of an algorithm for the automated numerical calculation of spin- and colour-correlated Born matrix elements in QCD. These spin- and colour-correlated matrix elements are needed for NLO calculations in combination with the subtraction method. Both massless and massive quarks are considered. There are no restrictions on the number of external particles. As a trivial sub-case, the algorithm also applies to Born matrix elements without any correlations. These are sufficient for leading order calculations.
description: 28 pages
Accessing new magnetic regimes by tuning the ligand spin-orbit coupling in van der Waals magnets
Creators: name: Tartaglia, Thomas A.
name: Tang, Joseph N.
name: Lado, Jose L.
name: Bahrami, Faranak
name: Abramchuk, Mykola
name: McCandless, Gregory T.
name: Doyle, Meaghan C.
name: Burch, Kenneth S.
name: Ran, Ying
name: Chan, Julia Y.
name: Tafti, Fazel
Publisher: name: arXiv
Year: 2020
Subjects: subject: Materials Science (cond-mat.mtrl-sci)
subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: FOS: Physical sciences

description: Van der Waals (VdW) materials have opened new directions in the study of low dimensional magnetism. A largely unexplored arena is the intrinsic tuning of VdW magnets toward new ground-states. The chromium trihalides provided the first such example with a change of inter-layer magnetic coupling emerging upon exfoliation. Here, we take a different approach to engineer new ground-states, not by exfoliation, but by tuning the spin-orbit coupling (SOC) of the non-magnetic ligand atoms (Cl,Br,I). We synthesize a three-halide series, CrCl$_{3-x-y}$Br$_{x}$I$_{y}$, and map their magnetic properties as a function of Cl, Br, and I content. The resulting triangular phase diagrams unveil a frustrated regime near CrCl$_{3}$. First-principles calculations confirm that the frustration is driven by a competition between the chromium and halide SOCs. Furthermore, we reveal a field-induced change of inter-layer coupling in the bulk of CrCl$_{3-x-y}$Br$_{x}$I$_{y}$ crystals at the same field as in the exfoliation experiments.
description: 22 pages, 6 figures
Table S3: from Fingers zipped up or baby mittens? Two main tetrapod strategies to return to the sea
Creators: name: Fernández, Marta S.
name: Vlachos, Evangelos
name: Buono, Mónica R.
name: Alzugaray, Lucia
name: Lisandro Campos
name: Sterli, Juliana
name: Herrera, Yanina
name: Paolucci, Florencia
Publisher: name: The Royal Society
Year: 2020
Subjects: subject: Evolutionary Biology
subject: FOS: Biological sciences
subject: 40308 Palaeontology (incl. Palynology)
subject: FOS: Earth and related environmental sciences
subject: 60301 Animal Systematics and Taxonomy
subject: 60310 Plant Systematics and Taxonomy

description: Information on the various runs to calculate the modularity Q and the Parcellation P.
Determinants of Farmers' Resilience towards ENSO-Related Drought: Evidence from Central Sulawesi, Indonesia
Creators: name: Keil, Alwin
name: Zeller, Manfred
name: Wida, Anastasia
name: Sanim, Bunasor
name: Birner, Regina
name: Keil, Alwin
name: Zeller, Manfred
name: Wida, Anastasia
name: Sanim, Bunasor
name: Birner, Regina
Publisher: name: Unknown
Year: 2006
Subjects: subject: Farm Management
subject: ENSO
subject: drought resilience
subject: risk management
subject: technical efficiency
subject: Indonesia

description: Crop production in the tropics is subject to considerable climate variability caused by the El Nino-Southern Oscillation (ENSO) phenomenon. In Southeast Asia, El Niño causes comparatively dry conditions leading to substantial declines of crop yields. In concert with global warming, the frequency and severity of the phenomenon are likely to increase during the 21st century. Little is known about the impact of ENSO-related drought on the welfare of farm households in developing countries. This paper seeks to contribute to closing this knowledge gap with a case study from Central Sulawesi, Indonesia. Its objective is to measure household resilience towards drought periods and identify its influencing factors to deduce policy implications. Using consumption-related indicators, we develop an index measuring household drought resilience; we then identify its determinants applying an asset-based livelihood framework encompassing the household-specific level of technical efficiency in agricultural production. Most of the drought-affected farm households are forced to substantially reduce expenditures for basic necessities, whereby the drastic cuts in food expenditures are particularly alarming. Households' drought resilience is strengthened by the possession of liquid assets, access to credit, and a high level of technical efficiency in crop production. The results suggest a number of policy recommendations, namely the improvement of the farmers' access to ENSO forecasts, the provision of formal credit at moderate interest rates to facilitate consumption smoothing, and the intensification of agricultural extension efforts in view of low levels of technical efficiency found in agricultural production.
Productivity Change in the Australian Sheep Industry Revisited
Creators: name: Villano, Renato A.
name: Fleming, Euan M.
name: Farrell, Terence C.
name: Fleming, Pauline
name: Villano, Renato A.
name: Fleming, Euan M.
name: Farrell, Terence C.
name: Fleming, Pauline
Publisher: name: Unknown
Year: 2006
Subjects: subject: Livestock Production/Industries
subject: Productivity Analysis
subject: sheep
subject: stochastic output distance function
subject: technical change
subject: total factor productivity

description: Recent low estimates of total factor productivity change for wool producers in the Australian sheep industry indicate that they are struggling to improve their performance. This evidence is at odds with the views of many technical observers of industry performance, prompting us to re-estimate total factor productivity change for farmers in a benchmarking group in south-west Victoria who had been the subject of such a negative finding. An important transformation in sheep production in Australia in recent decades has been a change in enterprise mix, notably a greater presence of prime lamb production. This change complicates the process of computing efficiency and productivity change. We demonstrate that a multi-input multi-output approach, based on the use of a stochastic output distance function, is essential to avoid errors of estimation of productivity change. Following this approach, we find substantial technical progress and productivity gains on farms over the period, 1995/1996 to 2003/2004. Growth in total factor productivity on both specialist wool-producing properties and properties operating wool and prime lamb enterprises averaged around an estimated 5 per cent per annum over the study period.
Controlling the helicity of magnetic skyrmions by electrical field in frustrated magnets
Creators: name: Yao, Xiaoyan
name: Chen, Jun
name: Dong, Shuai
Publisher: name: arXiv
Year: 2020
Subjects: subject: Materials Science (cond-mat.mtrl-sci)
subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: FOS: Physical sciences

description: The skyrmions generated by frustration in centrosymmetric structures host extra internal degrees of freedom: vorticity and helicity, resulting in distinctive properties and potential functionality, which are not shared by the skyrmions stemming from the Dzyaloshinskii-Moriya interaction in noncentrosymmetric structures. The present work indicates that the magnetism-driven electric polarization carried by skyrmions provides a direct handle for tuning helicity. Especially for the in-plane magnetized skyrmions, the helicity can be continuously rotated and exactly picked by applying an external electric field for both skyrmions and antiskyrmions. The in-plane uniaxial anisotropy is beneficial to this manipulation.
description: 5 figures
A Measurement of the CMB Spectrum from the 2003 Flight of BOOMERANG
Creators: name: Montroy, T. E.
name: Ade, P. A. R.
name: Bock, J. J.
name: Bond, J. R.
name: Borrill, J.
name: Boscaleri, A.
name: Cabella, P.
name: Contaldi, C. R.
name: Crill, B. P.
name: de Bernardis, P.
name: De Gasperis, G.
name: de Oliveira-Costa, A.
name: De Troia, G.
name: di Stefano, G.
name: Hivon, E.
name: Jaffe, A. H.
name: Kisner, T. S.
name: Jones, W. C.
name: Lange, A. E.
name: Masi, S.
name: Mauskopf, P. D.
name: MacTavish, C. J.
name: Melchiorri, A.
name: Natoli, P.
name: Netterfield, C. B.
name: Pascale, E.
name: Piacentini, F.
name: Pogosyan, D.
name: Polenta, G.
name: Prunet, S.
name: Ricciardi, S.
name: Romeo, G.
name: Ruhl, J. E.
name: Santini, P.
name: Tegmark, M.
name: Veneziani, M.
name: Vittorio, N.
Publisher: name: arXiv
Year: 2005
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: We report measurements of the CMB polarization power spectra from the January 2003 Antarctic flight of BOOMERANG. The primary results come from six days of observation of a patch covering 0.22% of the sky centered near R.A. = 82.5 deg., Dec= -45 deg. The observations were made using four pairs of polarization sensitive bolometers operating in bands centered at 145 GHz. Using two independent analysis pipelines, we measure a non-zero signal in the range 100< l <1000 with a significance 4.8-sigma, a 2-sigma upper limit of 8.6 uK^2 for any contribution, and a 2-sigma upper limit of 7.0 uK^2 for the spectrum. Estimates of foreground intensity fluctuations and the non-detection of and signals rule out any significant contribution from galactic foregrounds. The results are consistent with a Lambda-CDM cosmology seeded by adiabatic perturbations. We note that this is the first detection of CMB polarization with bolometric detectors.
description: Submitted to Astrophysical Journal
Prime Running Functions
Creators: name: Kim, Jaeyoon
Publisher: name: arXiv
Year: 2020
Subjects: subject: Number Theory (math.NT)
subject: FOS: Mathematics
subject: 11N13 (Primary) 11N05, 11N69 (Secondary)

description: We study arithmetic functions $Φ(x;d,a)$, called prime running functions, whose value at $x$ sums the gaps between primes $p_k \equiv a\ (\text{mod}\ d)$ below $x$ and the next following prime $p_{k+1}$, up to $x$. (The following prime $p_{k+1}$ may be in any residue class $(\text{mod}\ d)$.) We empirically observe systematic biases of order $x / \log x$ in $Φ(x;d,a) - Φ(x;d,b)$ for different $a,b$. We formulate modified Cramér models for primes and show that the corresponding sum of prime gap statistics exhibits systematic biases of this order of magnitude. The predictions of such modified Cramér models are compared with the experimental data.
description: Accepted by Experimental Mathematics (06-21-2020)
Outdoor education : subtitle a dialogue between theory and practice and implementation suggestions for the Discovery 10 program at St. George’s School
Creators: name: Piller, Neil
Publisher: name: University of British Columbia
Year: 2009

description: The field of outdoor education offers noble aims of making improvements in people's lives for the ultimate betterment of society (Hahn in Cousins, 2000). Yet, despite these lofty aims there is a general lack of clarity as to exactly what outcomes outdoor education is capable of achieving and by what processes these outcomes might be achieved. Drawing on personal experience and a review of the literature, a program design model is used to collate data in four areas: personal/interpersonal development; environmental awareness, ethics and stewardship; academic improvement; and the acquisition of outdoor skills and physical fitness. An analysis of this data provides program recommendations and suggestions for implementation. Specifically, this thesis examines the possibility of using the findings from theory and personal experience to inform the design of the Discovery 10 program at St. George's School. A number of factors relating to the transferability of findings to other programs are also considered.
A note on the natural density of product sets
Creators: name: Bettin, Sandro
name: Koukoulopoulos, Dimitris
name: Sanna, Carlo
Publisher: name: arXiv
Year: 2020
Subjects: subject: Number Theory (math.NT)
subject: Combinatorics (math.CO)
subject: FOS: Mathematics

description: Given two sets of natural numbers $\mathcal{A}$ and $\mathcal{B}$ of natural density $1$ we prove that their product set $\mathcal{A}\cdot \mathcal{B}:=\{ab:a\in\mathcal{A},\,b\in\mathcal{B}\}$ also has natural density $1$. On the other hand, for any $\varepsilon>0$, we show there are sets $\mathcal{A}$ of density $>1-\varepsilon$ for which the product set $\mathcal{A}\cdot\mathcal{A}$ has density $
description: 6 pages
Norm estimates of the partial derivatives for harmonic mappings and harmonic quasiregular mappings
Creators: name: Zhu, Jian-Feng
Publisher: name: arXiv
Year: 2020
Subjects: subject: Complex Variables (math.CV)
subject: FOS: Mathematics
subject: F.2.2; I.2.7
subject: Primary 30C55, 30C62

description: Suppose $p\geq1$, $w=P[F]$ is a harmonic mapping of the unit disk $\mathbb{D}$ satisfying $F$ is absolutely continuous and $\dot{F}\in L^p(0, 2π)$, where $\dot{F}(e^{it})=\frac{\mathrm{d}}{\mathrm{d}t}F(e^{it})$. In this paper, we obtain Bergman norm estimates of the partial derivatives for $w$, i.e., $\|w_z\|_{L^p}$ and $\|\overline{w_{\bar{z}}}\|_{L^p}$, where $1\leq p<2$. Furthermore, if $w$ is a harmonic quasiregular mapping of $\mathbb{D}$, then we show that $w_z$ and $\overline{w_{\bar{z}}}$ are in the Hardy space $H^p$, where $1\leq p\leq\infty$. The corresponding Hardy norm estimates, $\|w_z\|_{p}$ and $\|\overline{w_{\bar{z}}}\|_{p}$, are also obtained.
description: 17 pages
NGO Microfinance in Vietnam: Stakeholders' Perceptions of Effectiveness
Creators: name: Nghiem, Son
name: Laurenceson, James
name: Nghiem, Son
name: Laurenceson, James
Publisher: name: Unknown
Year: 2006
Subjects: subject: Financial Economics
subject: Microfinance
subject: NGO
subject: Vietnam
subject: perceptions
subject: effectiveness

description: The microfinance industry in Vietnam, particularly those sponsored by nongovernment organisations (NGOs), has experienced rapid expansion in recent years. Yet in spite of this growth, an analysis of their effectiveness has been lacking. In a bid to help address this shortcoming, this paper reports on a subset of data that was obtained during a survey and interview process that incorporated various stakeholders including financial donors, NGO-sponsored microfinance institutions (NMPs), village leaders and NMP members and non-members. Perceptions of NMPs effectiveness are discussed from the standpoint of various stakeholders. NMPs are found to be at a critical juncture. While their activities are widely perceived to contribute to poverty alleviation, their future viability is clouded by donor requirements that they become financially self-sufficient and at the same time certain government policies are making achieving this goal difficult.
Electron transport in a Pt-CO-Pt nanocontact: First-principles calculations
Creators: name: Strange, M.
name: Thygesen, K. S.
name: Jacobsen, K. W.
Publisher: name: arXiv
Year: 2005
Subjects: subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: FOS: Physical sciences

description: We have performed first-principles calculations for the mechanic and electric properties of pure Pt nano-contacts and a Pt contact with a single CO molecule adsorbed. For the pure Pt contacts we see a clear difference between point contacts and short chains in good agreement with experiments. We identify a tilted bridge configuration for the Pt-CO-Pt contact, which is stable and has a conductance close to $0.5G_0$ ($G_0=2e^2/h$), and we propose that this structure is responsible for an observed peak at $0.5G_0$ in the conductance histogram for Pt exposed to a CO gas. We explain the main features of the transmission function for the Pt-CO-Pt contact, and show that the conductance is largely determined by the local $d$-band at the Pt apex atoms.
description: 8 pages, 7 figures
The Initial Impact of WTO Membership on China's Trade Performance in Primary Agricultural And Processed Food Products
Creators: name: Xue, Liu
name: Revell, Brian J.
name: Zetian, Fu
name: Xue, Liu
name: Revell, Brian J.
name: Zetian, Fu
Publisher: name: Unknown
Year: 2006
Subjects: subject: International Relations/Trade
subject: China
subject: agricultural
subject: processed foods
subject: exports
subject: competitiveness

description: There has been much analysis of the potential impact of China's membership of the WTO on world trade in agricultural products but few studies of the actual effects thus far on China's trade performance. This paper compares changes in the competitiveness of China's trade in primary agricultural food and processed food products over the period 1998 to 2003 through a range of comparative advantage measures, the preferred being Revealed Symmetric Comparative Advantage. It also decomposes changes in China's export market share of these products over the period into structural and performance components and identifies where shifts in the global regional distribution of its exports have contributed to changes in its overall market share.
Direct Visualization of Irreducible Ferrielectricity in Crystals
Creators: name: Du, Kai
name: Guo, Lei
name: Peng, Jin
name: Chen, Xing
name: Zhou, Zheng-Nan
name: Zhang, Yang
name: Zheng, Ting
name: Liang, Yan-Ping
name: Lu, Jun-Peng
name: Ni, Zhen-Hua
name: Wang, Shan-Shan
name: Van Tendeloo, Gustaaf
name: Zhang, Ze
name: Dong, Shuai
name: Tian, He
Publisher: name: arXiv
Year: 2020
Subjects: subject: Materials Science (cond-mat.mtrl-sci)
subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: Superconductivity (cond-mat.supr-con)
subject: FOS: Physical sciences

description: In solids, charge polarity can one-to-one correspond to spin polarity phenomenologically, e.g. ferroelectricity/ferromagnetism, antiferroelectricity/antiferromagnetism, and even dipole-vortex/magnetic-vortex, but ferrielectricity/ferrimagnetism kept telling a disparate story in microscopic level. Since the definition of a charge dipole involves more than one ion, there may be multiple choices for a dipole unit, which makes most ferrielectric orders equivalent to ferroelectric ones, i.e. this ferrielectricity is not necessary to be a real independent branch of polarity. In this work, by using the spherical aberration-corrected scanning transmission electron microscope, we visualize a nontrivial ferrielectric structural evolution in BaFe2Se3, in which the development of two polar sub-lattices is out-of-sync, for which we term it as irreducible ferrielectricity. Such irreducible ferrielectricity leads to a non-monotonic behavior for the temperature-dependent polarization, and even a compensation point in the ordered state. Our finding unambiguously distinguishes ferrielectrics from ferroelectrics in solids.
description: 15 figures
The dimension monoid of a lattice
Creators: name: Wehrung, Friedrich
Publisher: name: arXiv
Year: 2005
Subjects: subject: General Mathematics (math.GM)
subject: FOS: Mathematics
subject: 06B05, 06B10, 06C10, 06C20, 20M14, 28B10, 16E50, 19A49

description: We introduce the dimension monoid of a lattice L, denoted by Dim L. The monoid Dim L is commutative and conical, the latter meaning that the sum of any two nonzero elements is nonzero. Furthermore, Dim L is given along with the dimension map, $\Dim$, from L x L to Dim L, which has the intuitive meaning of a distance function. The maximal semilattice quotient of Dim L is isomorphic to the semilattice Conc L of compact congruences of L; hence Dim L is a precursor of the congruence lattice of L. Here are some additional features of this construction: (1) Our dimension theory provides a generalization to all lattices of the von Neumann dimension theory of continuous geometries. In particular, if L is an irreducible continuous geometry, then Dim L is either isomorphic to Z^+ or to R^+. (2) If L has no infinite bounded chains, then Dim L embeds (as an ordered monoid) into a power of Z^+ $\cup$ {$\infty$}. (3) If L is modular or if L has no infinite bounded chains, then Dim L is a refinement monoid. (4) If L is a simple geometric lattice, then DimL is isomorphic to Z^+, if L is modular, and to the two-element semilattice, otherwise. (5) If L is a countably meet-continuous complemented modular lattice, then both Dim L and the dimension function $\Dim$ satisfy (countable) completeness properties. If R is a von Neumann regular ring and if L is the lattice of principal right ideals of the matrix ring M\_2(R), then Dim L is isomorphic to the monoid V(R) of isomorphism classes of finitely generated projective right R-modules. Hence the dimension theory of lattices provides a wide lattice-theoretical generalization of nonstable K-theory of regular rings.
Agriculture, Income Risks and Rural Poverty Dynamics: Strategies of Smallholder Producers in Kenya
Creators: name: Kuyiah, Joanne Wasswa
name: Obare, Gideon A.
name: Herrero, Mario
name: Waithaka, Michael M.
name: Kuyiah, Joanne Wasswa
name: Obare, Gideon A.
name: Herrero, Mario
name: Waithaka, Michael M.
Publisher: name: Unknown
Year: 2006
Subjects: subject: Farm Management
subject: Smallholder farms
subject: Income risk
subject: Rural Poverty
subject: Linear Programming
subject: Kenya

description: Poverty in Kenya has been on the increase over the last decade. It is estimated that 56% of the total population live in absolute poverty. Most of the poor reside in rural areas where agriculture is the main livelihood activity. Majority of Kenya's farmers are smallholders. They account for 75% of the total agricultural output and about 70% of marketed agricultural produce. The fate of smallholder agriculture in this country is therefore central to poverty reduction. A collapse in output and incomes from smallholder agriculture is likely to have damaging welfare effects and retard pro-poor economic growth. Smallholders often operate in a risky environment, which affects the level and variability of household resource endowments and income. The importance of risk analysis in smallholder production systems arises from the fact that strategies to help farmers raise their productivity and income require an understanding of how risk affects their production decisions. Using cross-sectional input-output data from 240 randomly selected households from Vihiga and Kilifi districts covering the 2003/4 agricultural year, and time series data on yields, this study investigates how risk affects farmers' production choices in the crop-livestock systems. Further, it explores the possibility of improving production and income on these smallholder farms. Linear programming and MOTAD are used in analysis. Results indicate there is potential to improve production and income on these smallholder farms through a change in the enterprise mix. The farm plans are sensitive to risk, with trade-offs occurring between higher risk and returns.
Romanian Maize - Distorted Prices and Producer Efficiency
Creators: name: Sauer, Johannes
name: Balint, Borbala
name: Sauer, Johannes
name: Balint, Borbala
Publisher: name: Unknown
Year: 2006
Subjects: subject: Crop Production/Industries
subject: Efficiency
subject: Shadow Cost Frontier
subject: Functional Consistency
subject: Maize
subject: Romania

description: This research aims at shedding empirical light on the relative efficiency of small-scale maize producers in Romania. Farmers in transition countries still face heavily distorted price systems resulting from imperfect market conditions and socioeconomic and institutional constraints. To capture such distortions we formulate a stochastic shadow-cost frontier model to investigate the systematic input-specific allocative inefficiency. We further adjust the underlying cost frontier by incorporating shadow price corrections and subsequently reveal evidence on farm specific technical inefficiency. Different models are estimated due to the imposition of curvature correctness and the effects on the individual efficiency estimates are shown. The empirical results show a relative high technical efficiency of the small-scale farmers but relatively poor scores on systematic input price efficiency. The usage of extension services as well as agricultural training on the farm level are found to have a positive effect on the technical efficiency level of the farms. All model specifications further agree on the negative effect on efficiency with respect to the use of insecticides. The imposition of functional concavity on the shadow cost frontier leads to relative differences in the efficiency estimates of up to 240%.
Orbital ordering in cubic LaMnO3 from first principles calculations
Creators: name: Zenia, H.
name: Gehring, G. A.
name: Temmerman, W. M.
Publisher: name: arXiv
Year: 2005
Subjects: subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: FOS: Physical sciences

description: We report on first principles Self-Interaction Corrected LSD (SIC-LSD) calculations of electronic structure of LaMnO$_{3}$ in the cubic phase. We found a strong tendency to localisation of the Mn $e_{g}$ electron and to orbital ordering. We found the ground state to be orbitally ordered with a staggered order of $x^{2}-z^{2}$ and $y^{2}-z^{2}$ orbits in one plane and this order is repeated along the third direction. The difference in energy with a solution consisting of the ordering of $3x^{2}-r^{2}$ and $3y^{2}-r^{2}$ is, however, very small. The latter ordering is similar to the one observed both experimentally and theoretically in the real distorted system. The system is in the insulating A-type antiferromagnetic ordered state in both cases. The presence of orbital ordering means breaking of the cubic symmetry and without recourse to distortion. The latter may rather be the result of the orbital ordering but the symmetry of this ordering is determined by coupling to the lattice. The strong tendency to localisation of the $e_{g}$ electron in LaMnO$_{3}$ accounts for the survival of local distortions above the structural phase transition temperature.
description: 6 pages, 5 figures and 3 tables
The Economics of Agricultural Development: What Have We Learned?
Creators: name: Roumasset, James A.
name: Roumasset, James A.
Publisher: name: Unknown
Year: 2006
Subjects: International Development

description: The history of thought in the field of Economic Development and corresponding development programs have gone through a series of identifiable phases. Phases of theory and praxis in Agricultural Development are likewise compared. In both cases, there is an apparent lost opportunity to learn the lessons of past failures and successes before moving to the next fad. After reviewing several policy and program areas, a few lessons are synthesized, a forward-looking research framework suggested, and the appropriate role of foreign aid discussed. A particular theme of interest is the balance in thinking and programs between social engineering and facilitation of economic cooperation.
Pervasiveness and Patterns of Non-tariff Measures Affecting EU Agri-food Exports
Creators: name: Walkenhorst, Peter
name: Walkenhorst, Peter
Publisher: name: Unknown
Year: 2004
Subjects: International Relations/Trade

description: Evaluating the importance of non-tariff measures (NTMs) remains a major challenge. This paper reports evidence on the prevalence of NTMs in the agri-food sector based on an EU inventory of business complaints. This data source has the advantage of drawing on experiences of economic agents that are directly involved in trading activities, of containing information on domestic governance issues, and of covering procedural aspects of NTMs. The results suggest that business complaints about price control measures, quantitative import controls, monopolistic measures, technical measures, and certification are particularly frequent.
Time-resolved fast turbulent dynamo in a laser plasma
Creators: name: Bott, A. F. A.
name: Tzeferacos, P.
name: Chen, L.
name: Palmer, C. A. J.
name: Rigby, A.
name: Bell, A.
name: Bingham, R.
name: Birkel, A.
name: Graziani, C.
name: Froula, D. H.
name: Katz, J.
name: Koenig, M.
name: Kunz, M. W.
name: Li, C. K.
name: Meinecke, J.
name: Miniati, F.
name: Petrasso, R.
name: Park, H. -S.
name: Remington, B. A.
name: Reville, B.
name: Ross, J. S.
name: Ryu, D.
name: Ryutov, D.
name: Séguin, F.
name: White, T. G.
name: Schekochihin, A. A.
name: Lamb, D. Q.
name: Gregori, G.
Publisher: name: arXiv
Year: 2020
Subjects: subject: Plasma Physics (physics.plasm-ph)
subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences

description: Understanding magnetic-field generation and amplification in turbulent plasma is essential to account for observations of magnetic fields in the universe. A theoretical framework attributing the origin and sustainment of these fields to the so-called fluctuation dynamo was recently validated by experiments on laser facilities in low-magnetic-Prandtl-number plasmas ($\mathrm{Pm} < 1$). However, the same framework proposes that the fluctuation dynamo should operate differently when $\mathrm{Pm} \gtrsim 1$, the regime relevant to many astrophysical environments such as the intracluster medium of galaxy clusters. This paper reports a new experiment that creates a laboratory $\mathrm{Pm} \gtrsim 1$ plasma dynamo for the first time. We provide a time-resolved characterization of the plasma's evolution, measuring temperatures, densities, flow velocities and magnetic fields, which allows us to explore various stages of the fluctuation dynamo's operation. The magnetic energy in structures with characteristic scales close to the driving scale of the stochastic motions is found to increase by almost three orders of magnitude from its initial value and saturate dynamically. It is shown that the growth of these fields occurs exponentially at a rate that is much greater than the turnover rate of the driving-scale stochastic motions. Our results point to the possibility that plasma turbulence produced by strong shear can generate fields more efficiently at the driving scale than anticipated by idealized MHD simulations of the nonhelical fluctuation dynamo; this finding could help explain the large-scale fields inferred from observations of astrophysical systems.
description: 12 pages, 9 figures
Carbon sequestration through the planting of multi-annual energy crops: A dynamic and spatial assessment
Creators: name: De Cara, Stephane
name: Rozakis, Stelios
name: De Cara, Stephane
name: Rozakis, Stelios
Publisher: name: Unknown
Year: 2004
Subjects: Crop Production/Industries

description: In this study, we examine the spatial and dynamic implications of policies aimed at increasing carbon sequestration in agricultural soils. We consider incentive mechanisms designed to encourage the planting of energy multi-annual crops that allow higher carbon sequestration rates for a longer period of time. By using a dynamic micro-economic model, we simulate the sequence of crop plantings over a given time horizon and investigate different payment mechanisms (per-ton or per-hectare). We discuss their implications in terms of regulation policy and efficiency. This model is then applied to the Central Plains of Thessaly, Greece, to assess the marginal costs of carbon sequestration and the optimal timing of switching to multi-annual energy crops. To do so, we combine the dynamic microeconomic model with a carbon accounting model and a geophysical database. We assess the efficiency loss of constant per-hectare payments compared to per-ton mechanisms. The dynamic and spatial implications of these mechanisms are compared and discussed.
Study of the strong $Σ_c\to Λ_c π$, $Σ_c^{*}\to Λ_c π$ and $Ξ_c^{*}\to Ξ_c π$ decays in a nonrelativistic quark model
Creators: name: Albertus, C.
name: Hernandez, E.
name: Nieves, J.
name: Verde-Velasco, J. M.
Publisher: name: arXiv
Year: 2005
Subjects: subject: High Energy Physics - Phenomenology (hep-ph)
subject: Nuclear Theory (nucl-th)
subject: FOS: Physical sciences

description: We present results for the strong widths corresponding to the $Σ_c\to Λ_c π$, $Σ_c^{*}\to Λ_c π$ and $Ξ_c^{*}\to Ξ_c π$ decays. The calculations have been done in a nonrelativistic constituent quark model with wave functions that take advantage of the constraints imposed by heavy quark symmetry. Partial conservation of axial current hypothesis allows us to determine the strong vertices from an analysis of the axial current matrix elements. Our results \hbox{$Γ(Σ_c^{++}\to Λ_c^+ π^+)=2.41 \pm0.07\pm0.02 \mathrm{MeV}$}, {$Γ(Σ_c^{+}\to Λ_c^+ π^0)=2.79 \pm0.08\pm0.02 \mathrm{MeV}$}, {$Γ(Σ_c^{0}\to Λ_c^+ π^-)=2.37 \pm0.07\pm0.02 \mathrm{MeV}$}, {$Γ(Σ_c^{* ++}\to Λ_c^+ π^+)=17.52\pm0.74\pm0.12 \mathrm{MeV}$}, {$Γ(Σ_c^{* +}\to Λ_c^+ π^0)=17.31\pm0.73\pm0.12 \mathrm{MeV}$}, {$Γ(Σ_c^{* 0}\to Λ_c^+ π^-)=16.90\pm0.71\pm0.12 \mathrm{MeV}$}, {$Γ(Ξ_c^{* +}\to Ξ_c^0 π^++Ξ_c^+π^0)=3.18\pm0.10\pm0.01 \mathrm{MeV}$} and {$Γ(Ξ_c^{* 0}\to Ξ_c^+ π^-+Ξ_c^0π^0)=3.03\pm0.10\pm0.01 \mathrm{MeV}$} are in good agreement with experimental determinations.
description: 8 latex pages. Shortened version accepted for publication in Physical Review D
A superconducting praseodymium nickelate with infinite layer structure
Creators: name: Osada, Motoki
name: Wang, Bai Yang
name: Goodge, Berit H.
name: Lee, Kyuho
name: Yoon, Hyeok
name: Sakuma, Keita
name: Li, Danfeng
name: Miura, Masashi
name: Kourkoutis, Lena F.
name: Hwang, Harold Y.
Publisher: name: arXiv
Year: 2020
Subjects: subject: Superconductivity (cond-mat.supr-con)
subject: Materials Science (cond-mat.mtrl-sci)
subject: FOS: Physical sciences

description: A variety of nickel oxide compounds have long been studied for their manifestation of various correlated electron phenomena. Recently, superconductivity was observed in nanoscale infinite layer nickelate thin films of Nd$_{0.8}$Sr$_{0.2}$NiO$_2$, epitaxially stabilized on SrTiO$_3$ substrates via topotactic reduction from the perovskite precursor phase. Here we present the synthesis and properties of PrNiO$_2$ thin films on SrTiO$_3$. Upon doping in Pr$_{0.8}$Sr$_{0.2}$NiO$_2$, we observe superconductivity with a transition temperature of 7-12 K, and robust critical current density at 2 K of 334 kA/cm$^2$. These findings indicate that superconductivity in the infinite layer nickelates is relatively insensitive to the details of the rare earth 4$f$ configuration. Furthermore, they motivate the exploration of a broader family of compounds based on two-dimensional NiO$_2$ planes, which will enable systematic investigation of the superconducting and normal state properties and their underlying mechanisms.
description: 19 pages, 4 figures
A Panel Data Approach to the Measurement of Technical Efficiency and its Determinants: Some Evidence from the Tunisian Agro-Food Industry
Creators: name: Lachaal, Lassaad
name: Chebil, Ali
name: Dhehibi, Boubaker
name: Lachaal, Lassaad
name: Chebil, Ali
name: Dhehibi, Boubaker
Publisher: name: Unknown
Year: 2004
Subjects: Research and Development/Tech Change/Emerging Technologies

description: This study investigates firm level technical efficiency of production and its determinants in the Tunisian agro-food industry. To this end, a stochastic production frontier model, in which technical efficiency effects are assumed to be a function of firm-specific variables and time, is estimated using panel data on 46 agro-food firms observed over a period of 14 years. Results indicate that technical efficiency in the sample of firms investigated ranges from a minimum of 45% to a maximum of 90% with an average technical efficiency estimate of 67%. Further, investigation of the sources of technical inefficiency in the sample reveals that the age of capital stock and firm size are negatively associated with efficiency, the share of skilled labour is positively associated with efficiency and, on average, technical efficiency tendes to decline during the period of investigation.
Table S1: from Fingers zipped up or baby mittens? Two main tetrapod strategies to return to the sea
Creators: name: Fernández, Marta S.
name: Vlachos, Evangelos
name: Buono, Mónica R.
name: Alzugaray, Lucia
name: Lisandro Campos
name: Sterli, Juliana
name: Herrera, Yanina
name: Paolucci, Florencia
Publisher: name: The Royal Society
Year: 2020
Subjects: subject: Evolutionary Biology
subject: FOS: Biological sciences
subject: 40308 Palaeontology (incl. Palynology)
subject: FOS: Earth and related environmental sciences
subject: 60301 Animal Systematics and Taxonomy
subject: 60310 Plant Systematics and Taxonomy

description: List of the specimens used for the construction of the anatomical networks of the forefins, and their networks.
The impact of the EU Water Framework Directive on irrigated agriculture in Italy: the case of the North-East fruit district
Creators: name: Bazzani, Guido Maria
name: Di Pasquale, S.
name: Gallerani, Vittorio
name: Morganti, S.
name: Raggi, Meri
name: Viaggi, Davide
name: Bazzani, Guido Maria
name: Di Pasquale, S.
name: Gallerani, Vittorio
name: Morganti, S.
name: Raggi, Meri
name: Viaggi, Davide
Publisher: name: Unknown
Year: 2004
Subjects: Crop Production/Industries

description: The objective of the paper is to evaluate the sustainability of irrigated agriculture under Water Framework Directive (60/2000) and Agenda 2000. The methodology relies on scenario analysis combined to farm level multicriteria mathematical programming. The methodology is applied to the case study of fruit farming in Northern Italy. The research shows that water pricing can improve irrigation efficiency, but the impact of water policy is strongly affected by agricultural policy scenarios. In order to make water policies more socially sound, it is necessary to consider a broader range of impacts and to provide a higher co-ordination between policy goals.
Proper congruence-preserving extensions of lattices
Creators: name: Grätzer, George
name: Wehrung, Friedrich
Publisher: name: arXiv
Year: 2005
Subjects: subject: General Mathematics (math.GM)
subject: FOS: Mathematics
subject: 06B10, 08A30

description: We prove that every lattice with more than one element has a proper congruence-preserving extension.