737 research outputs found
Transport properties of HTS cuprates via spin-charge gauge approach
No full textWe show that the spin–charge gauge approach to the 2D t–J model can naturally explain many experimental features of transport properties for HTS cuprates, in particular temperature crossover phenomena in the “pseudogap phase” (PG) and 1/T behavior of conductivities in the “strange metal phase” (SM) at higher T or x (doping concentration)
Hole pairing from attraction of opposite-chirality spin vortices: Non-BCS superconductivity in underdoped cuprates
No full textWithin a gauge approach to the t-J model, we propose a non-BCS mechanism of superconductivity (SC) for underdoped cuprates. We implement the no-double-occupancy constraint with a (semionic) slave-particle formalism. The dopant in the t-J model description generates a vortexlike quantum distortion of the antiferromagnetic (AF) background centered on the empty sites, with opposite chirality for cores on the two Néel sublattices. Empty sites are described in terms of spinless fermionic holons and the long-range attraction between spin vortices on two opposite Néel sublattices serves as the holon pairing force, leading eventually to SC. The spin fluctuations are described by bosonic spinons with a gap generated by scattering on spin vortices. Due to the no-double occupation constraint, there is a gauge attraction between holon and spinon, binding them into a physical hole. Through gauge interaction the spin-vortex attraction induces the formation of spin-singlet [resonance valence bond (RVB)] spin pairs by lowering the spinon gap, due to the appearance of spin-vortex dipoles. Lowering the temperature, the proposed approach anticipates two crossover temperatures as precursors of the SC transition: at the higher crossover a finite density of incoherent holon pairs are formed, leading to reduction of the hole spectral weight, while at the lower crossover a finite density of incoherent spinon RVB pairs is also formed, giving rise to a gas of incoherent preformed hole pairs with magnetic vortices appearing in the plasma phase, supporting a Nernst signal. Finally, at an even lower temperature the hole pairs become coherent, the magnetic vortices become dilute, and SC appears beyond a critical doping. The proposed SC mechanism is not of the BCS type, because it involves a gain in kinetic energy, due to the lowering of the spinon gap, and it is “almost” of the classical three-dimensional XY type. Since both the spinon gap describing short-range antiferromagnetism order, and the holon pairing generating SC, originate from the same term in the slave-particle representation of the t-J model, the proposed approach incorporates a strong interplay between antiferromagnetism and SC, giving rise to a universal relation between Tc and the energy of the resonance mode, as observed in neutron-scattering experiment
Non-BCS superconductivity for underdoped cuprates by spin-vortex attraction
No full textWithin a gauge approach to the t-J model, we propose a new, non-BCS mechanism of superconductivity for underdoped cuprates. The gluing force of the superconducting mechanism is an attraction between spin vortices on two different N\'eel sublattices, centered around the empty sites described in terms of fermionic holons. The spin fluctuations are described by bosonic spinons with a gap generated by the spin vortices. Due to the no-double occupation constraint, there is a gauge attraction between holon and spinon binding them into a physical hole. Through gauge interaction the spin vortex attraction induces the formation of spin-singlet (RVB) spin pairs with a owering of the spinon gap. Lowering the temperature the approach exhibits two crossover temperatures: at the higher crossover a finite density of incoherent holon pairs are formed leading to a reduction of the hole spectral weight, at the lower crossover also a finite density of incoherent spinon RVB pairs are formed, giving rise to a gas of incoherent preformed hole pairs, and magnetic vortices appear in the plasma phase. Finally, at a even lower temperature the hole pairs become coherent, the magnetic vortices become dilute and superconductivity appears. The superconducting mechanism is not of BCS-type since it involves a gain in kinetic energy (for spinons) coming from the spin interactions
Card-image public access catalogues (CIPACs) : Issues concerned with their planning and implementation
No full textThis article identifies and discusses the issues and problems that need to be considered in the process of planning and implementing card-image public access catalogues (CIPACs). CIPACs are online library catalogues based on databases of digitised catalogue cards with more or less sophisticated mechanisms for browsing or searching. Solutions of this kind have been implemented by a number of libraries in various countries since the mid-1990s, mainly as inexpensive alternatives to full retrospective conversion of their old catalogues. Based upon a questionnaire and relevant literature, the article looks at the following aspects: cost, conversion speed, universal access, saving of space, preservational aspects, software selection, preparing the card catalogue for conversion, scanning and quality control, image standards, optical character recognition, manual and intellectual input, technological aspects, administrative tools, organisational aspects, peculiarities of old catalogues, presentation of CIPACs to the users, and life expectancy of card-image catalogues
A non-BCS mechanism for superconductivity in underdoped cuprates via attraction between spin vortices
No full textWe propose a non-BCS mechanism for superconductivity in hole-underdoped cuprates based on a gauge approach to the t-J model. The gluing force is an attraction between spin vortices centered on the empty sites of two opposite N\'eel sublattices, leading to pairing of charge carriers. In the presence of these pairs, a gauge force coming from the single occupancy constraint induces, in turn, the pairing of the spin carriers. The combination of the charge and spin pairs gives rise to a finite density of incoherent hole pairs, leading to a finite Nernst signal as precursor to superconductivity. The true superconducting transition occurs at an even lower temperature, via a 3D XY-type transition. The main features of this non-BCS description of superconductivity are consistent with the experimental results in underdoped cuprates, especially the contour plot of the Nernst signal
Zb tetraquark channel and BB¯? interaction
No full text37th International Symposium on Lattice Field Theory, LATTICE 2019 -- 16 June 2019 through 22 June 2019 -- Wuhan -- 166411Two tetraquark candidates Zb(10610) and Zb(10650) with flavor structure bb ¯ du ¯ were discovered by Belle experiment in 2011. We present a preliminary Nf = 2 lattice study of the bb ¯ du ¯ system in the approximation of static b quarks, where the total spin of heavy quarks is fixed to one. The ground and the excited eigen-energies are determined as a function of separation r between b and b¯. The lower eigenstates are related to a bottomonium and a pion. One of the higher eigenstates is dominated by BB¯?: its energy is significantly below mB + mB? for r=[0.1,0.4] fm, which suggests sizable attraction. The attractive potential V(r) between B and B¯? is extracted assuming that this eigenstate is related exclusively to BB¯?. Assuming a certain form of the potential at small r < 0.1 fm and solving non-relativistic Schrodinger equation, we find a virtual bound state pole 32?+295 MeV below BB¯? threshold. This pole leads to a narrow peak in the cross-section just above threshold that could be perhaps related to experimental Zb resonances. Given all these approximations, we surprisingly find also a deep bound state 403 ±70 MeV below BB¯? threshold. If such a Zb state exists, it could be experimentally searched in the accurate dependence of rates on ?(1S)?+ invariant mass. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0).Research Agency ARRS, (J1-8137, P1-0035); TUBITAK; Deutsche Forschungsgemeinschaft, DFG; Türkiye Bilimsel ve Teknolojik Araştirma Kurumu, TÜBITA
ANALYSIS OF INVESTMENT FUNDS IN THE REPUBLIC OF CROATIA WITH A FOCUS ON QUANTITATIVE ANALYSIS OF OPERATIONS OF THE INVESTMENT COMPANY „ZB Invest“
No full textInvesticijski fondovi su institucionalni ulagači koji prikupljaju novčana sredstva široke javnosti (pojedinaca i kućanstava), ali i poduzeća i financijskih institucija te ih plasiraju u različite vrste imovine u cilju ostvarivanja prinosa. Iako su investicijski fondovi u Republici Hrvatskoj relativno nove financijske institucije koje su započele s djelovanjem tek sredinom devedesetih godina, bilježi se rast njihovog broja te neto vrijednosti imovine. U radu je dan osvrt na dvije vrste investicijskih fondova koji danas djeluju u Republici Hrvatskoj, a to su otvoreni investicijski fondovi s javnom ponudom (UCITS) i alternativni investicijski fondovi (AIF). Analiza dioničkih, obvezničkih, mješovitih i novčanih UCITS fondova koji se razlikuju prema ulagačkoj strukturi provodi se korištenjem znanstvenih metoda te grafičkog prikaza podataka. Posebna pozornost u radu pridaje se društvu „ZB invest“ te detaljnoj analizi ZB aktiv, ZB global, ZB bond i ZB plus pod-fondova korištenjem različitih kvantitativnih pokazatelja performansi. Time se ukazuje na različitost pojedinih fondova s obzirom na njihovu ulagačku strukturu, rizik i prinos, ali i atraktivnost ulaganja u investicijske fondove za pojedine profile ulagača. U ovom radu se koriste moderne mjere rizika kao što su VaR i CVaR za kvantitativnu analizu te izračunavanje i interpretiranje rizika. Na navedene mjere rizika potrebno je ukazati upravo zbog njihove popularnosti u modernim kvantitativnim istraživanjima slične tematike te manjka provedenih domaćih istraživanja pomoću navedenih mjera rizika. Tako dobiveni podatci o riziku investicijskih fondova uspoređuju se sa standardnom devijacijom prinosa kao tradicionalnom mjerom rizika kako bi se naglasila važnost izbora mjere rizika. Također, podaci o riziku dovode se u odnos sa prinosom investicijskih fondova koji su predmet analize kako bi se ispitala uvriježena povezanost između rizika i prinosa.Investment funds are institutional investors that raise funds from the general public (individuals and households), companies and financial institutions and place them in various types of assets in order to achieve returns. Although investment funds in the Republic of Croatia are relatively new financial institutions that started operating in the mid-1990s, their number and net asset value are increasing ever since. This paper refers to the two types of investment funds that operate in the Republic of Croatia today, namely open-end investment funds with a public offering (UCITS) and alternative investment funds (AIF). An analysis of equity, bond, mixed and money UCITS funds that differ according to their investment structure is conducted using scientific methods and graphical presentation of data. Special attention in this paper is given to the company "ZB invest" with detailed analysis of ZB aktiv, ZB global, ZB bond and ZB plus sub-funds using different quantitative performance indicators. This approach indicates the diversity of individual funds with regard to their investment structure, risk and return, but also the attractiveness of investing in investment funds for different profiles of investors. The paper uses modern risk measures such as VaR and CVaR for quantitative analysis and calculation and interpretation of risk. These risk measures need to be emphasized because of their popularity in modern quantitative research on similar topics and the lack of domestic research conducted using these risk measures. The risk data of investment funds thus obtained is compared with the standard deviation as a traditional risk measure in order to stress the importance of the risk measure selection. Also, risk data is observed in relation to the return of the analyzed investment funds to examine the ingrained relationship between risk and return
Cellular and molecular mechanisms of immuno-modulation by Ganoderma lucidum
No full textGanoderma lucidum (Leyss. ex Fr.) Karst. (Lingzhi or Reishi) has been used for a long time in China to prevent and treat various human diseases. G. lucidum polysaccharides extracted from G. lucidum are one of efficacious ingredient groups of G. lucidum. A number of reports have demonstrated that G. lucidum polysaccharides modulate immune function both in vivo and in vitro. The immuno-modulating effects of G. lucidum polysaccharides were extensive, including promoting the function of antigen-presenting cells, mononuclear phygocyte system, humoral immunity, and cellular immunity. Cellular and molecular mechanisms, possible receptors involved, and triggered signaling cascades have also been studied in vitro. However, whole animal experiments are still needed to further establish the mechanism of the immunomodulating effects by G. lucidum. Evidence-based clinical trials are also needed.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000232842900003&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Pharmacology & PharmacySCI(E)PubMed87REVIEW2144-1539
UCITS INVESTICIJSKI FONDOVI U REPUBLICI HRVATSKOJ NA PRIMJERU ZB INVEST D.O.O.
No full textUlaganje u investicijske fondove jedan je od najpopularnijih oblika ulaganja vlastitih sredstava s ciljem ostvarivanja prinosa. Prije samog procesa donošenja odluke neophodno je informirati se o vrstama fondova, njihovim karakteristikama, rizicima, kretanjima i svemu ostalom što je potrebno kako bi uspješno iskoristili sve beneficije koje fondovi nude. U ovom radu će se obraditi sve vrste fondova u Republici Hrvatskoj i to na primjeru fondova iz portfelja ZB Invest društva za upravljanjem investicijskim fondovima. Analizirat će se koje su sve okolnosti utjecale na kretanje u prošlim razdobljima jer upravo su ti podaci potrebni za dublje shvaćanje investicijskih fondova i rizika koji na njih mogu utjecati, a sve u svrhu donošenja uspješnih potencijalnih investicijskih odluka na temelju saznanja iz prethodnih razdoblja.Investing in investment funds is one of the most popular forms of investing in equity in order to generate returns. Prior to the decision-making process itself, it is necessary to be informed about the types of funds, their characteristics, risks, developments and everything else needed to successfully reap the full benefits of the funds. This paper will cover all types of funds in the Republic of Croatia, on the example of funds from the portfolio of ZB Invest Investment Management Company. It will analyze all the circumstances which had influence on the movement in the previous periods, because this information is needed for a deeper understanding of the investment funds and the risks that may be affected by them, with the purpose of making successful potential investment decisions based on the knowledge from previous periods
Evaluación de la implementación de ZigBee open-ZB
No full textZigBee es un protocolo de comunicaciones en redes inalámbricas diseñado para redes de sensores que requieren una baja velocidad de transmisión y un bajo consumo. Hay un gran número de aplicaciones que pueden incorporarlo: sistemas de seguridad, redes de control industrial, domótica...
Ofrece atributos de seguridad, permite numerosos nodos, y soporta interoperabilidad e independencia de los distribuidores. También incorpora características que permiten un rendimiento sobresaliente con un consumo de energía relativamente bajo.
A pesar de sus ventajas, no es libre, es decir, los desarrolladores no pueden descargarse su código fuente y realizar modificaciones sobre él.
Por esta razón, este trabajo de fin de carrera pretende evaluar una serie de códigos adaptados capaces de realizar algunas de las funciones de ZigBee.
Dichas evaluaciones se realizarán modificando los códigos que ofrece la implementación Open-ZB, cargándolos en los sensores TelosB y capturando los resultados mediante el analizador Perytons.
A lo largo de este documento se explicarán todos los conceptos necesarios para la comprensión del proyecto
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