1,003 research outputs found
On the analytical convergence of the QPA procedure
We present an analytical proof of the convergence of the ``quantum privacy
amplification'' procedure proposed by D. Deutsch et al. [Phys. Rev. Lett. 77,
2818 (1996)]. The proof specifies the range of states which can be purified by
this method.Comment: 3 pages (revtex), 1 figure, to appear in Phys. Lett.
Vertical Integration and Investor Protection in Developing Countries
The industrial organization of developing countries is characterized by the pervasive use of subcontracting arrangements among small, financially constrained firms. This paper asks whether vertical integration relaxes those financial constraints. It shows that vertical integration trades off the benefits of joint liability against the costs of rendering the supply chain more opaque to external investors. In contrast to the commonly held view that pervasive input and capital market imperfections are conducive to vertical integration, the model predicts that the motives for vertical integration are not necessarily higher in developing countries. In particular, vertical integration is more likely to arise at intermediate levels of investor protection and better contract enforcement with suppliers reduces vertical integration only if financial markets are sufficiently developed. Evidence supporting both predictions is discussed.Vertical Integration, Industrial Development, Financial Constraints, Joint Liability, Trade Credit, Community-based Industries
The value of relationships : evidence from a supply shock to Kenyan rose exports
This paper provides evidence on the importance of reputation, intended as beliefs buyers hold about seller's reliability, in the context of the Kenyan rose export sector. A model of reputation and relational contracting is developed and tested. We show that 1) the value of the relationship increases with the age of the relationship; 2) during an exogenous negative supply shock sellers prioritize relationships consistently with the predictions of the model; and 3) reliability at the time of the shock positively correlates with future survival and relationship
value. Models exclusively focussing on enforcement or insurance considerations cannot account for the evidence
Eficiencia de absorción de nutrientes de Gracilaria chilensis y Ulva lactuca en un sistema multitrófico integrado con el abalón rojo Haliotis rufescens
Indexación: Web of Science; Scielo.ABSTRACT. The current study examined the nutrient uptake efficiency of Ulva lactuca and Gracilaria chilensis cultivated in tanks associated with the wastewater of a land-based abalone culture. The experiments evaluated different seaweed stocking densities (1200, 1900, 2600, and 3200 g m-2) and water exchange rates (60, 80, 125, and 250 L h-1). The results show that both U. lactuca and G. chilensis were efficient in capturing and removing all of the inorganic nutrients originating from the abalone cultivation for all of the tested conditions. Furthermore, an annual experiment was performed with U. lactuca, cultivated at a stocking density of 1900 g m-2 and at a water exchanged rate of 125 L h-1, in order to evaluate seasonal changes in the nutrient uptake efficiency, productivity, and growth rate associated with the wastewater of a land-based abalone culture. The results confirmed high uptake efficiency during the entire year, equivalent to a 100% removal of the NH4, NO3, and PO4 produced by the land-based abalone culture. The growth rate and productivity of U. lactuca presented a marked seasonality, increasing from fall until summer and varying from 0.5 ± 0.2% to 2.6 ± 0.2% d-1 and 10 ± 6.1% to 73.6 ± 8.4% g m-2 d-1 for sustainable growth rate and productivity, respectively. We conclude that there is sufficient evidence that demonstrates the high possibility of changing the traditional monoculture system of abalone in Chile, to a sustainable integrated multi-trophic aquaculture system, generating positive environmental externalities, including the use of U. lactuca as a biofiltration unit.Resumen: Se analizó la eficiencia de captación de nutrientes de Ulva lactuca y Gracilaria chilensis, cultivadas en estanques asociados a aguas de desecho proveniente de un cultivo del abalón rojo Haliotis rufescens. Los experimentos consideraron evaluar diferentes densidades de cultivo de algas (1200, 1900, 2600 and 3200 g m-2) y tasas de recambio de agua (60, 80, 125 y 250 L h-1). Los resultados mostraron que tanto U. lactuca como G. chilensis fueron eficientes en la captación de nutrientes inorgánicos provenientes del cultivo de abalón, en todas las condiciones probadas, con remoción total de los nutrientes aportados por el cultivo. De la misma forma se realizó un experimento anual con U. lactuca, siendo cultivada con densidad de 1900 g m-2 y tasa de recambio de agua de 125 L h-1 para evaluar cambios estacionales en la eficiencia de captación de nutrientes, así como en la productividad y tasa de crecimiento de U. lactuca. Los resultados confirmaron una alta eficiencia de captación de U. lactuca durante todo el año, equivalente a la remoción del 100% del NH4, NO3 y PO4 aportado por el cultivo de abalón. La tasa de crecimiento y la productividad de U. lactuca presentó una marcada estacionalidad, incrementando de otoño al verano, variando de 0,5 ± 0,2 a 2,6 ± 0,2% d-1 y 10 ± 6,1 a 73,6 ± 8,4 g m-2 d-1, respectivamente. Se concluye que existen antecedentes suficientes que demuestran que es altamente posible cambiar la actividad tradicional de cultivo de abalón por un sistema integrado multitrófico, alcanzando externalidades ambientales positivas que incluyen U. lactuca como unidad de biofiltración.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-560X201400030001
Against Quantum Noise
This is a brief description of how to protect quantum states from dissipation
and decoherence that arise due to uncontrolled interactions with the
environment. We discuss recoherence and stabilisation of quantum states based
on two techniques known as "symmetrisation" and "quantum error correction". We
illustrate our considerations with the most popular quantum-optical model of
the system-environment interaction, commonly used to describe spontaneous
emission, and show the benefits of quantum error correction in this case.Comment: 12 pages. Presented at the International Conference "Quantum Optics
IV", Jaszowiec, Poland, June 17-24 1997. An introductory overview of quantum
dissipation and error correction. Late submission to the archive due to
requests and the limited availability of the journa
Noise robustness in the detection of non separable random unitary maps
We briefly review a recently proposed method to detect properties of quantum
noise processes and quantum channels. We illustrate in detail the method for
detecting non separable random unitary channels and consider in particular the
explicit examples of the CNOT and CZ gates. We analyse their robustness in the
presence of noise for several quantum noise models.Comment: 10 pages, 1 figur
Multipartite entanglement in quantum algorithms
We investigate the entanglement features of the quantum states employed in
quantum algorithms. In particular, we analyse the multipartite entanglement
properties in the Deutsch-Jozsa, Grover and Simon algorithms. Our results show
that for these algorithms most instances involve multipartite entanglement
Detection methods to rule out completely co-positive and bi-entangling operations
In this work we extend the quantum channel detection method developed in
[Phys. Rev. A 88, 042335 (2013)] and [Phys. Script. T153, 014044 (2013)] in
order to detect other interesting convex sets of quantum channels. First we
work out a procedure to detect non completely co-positive maps. Then we focus
on the set of so-called bi-entangling operations and show how a map outside
this set can be revealed. In both cases we provide explicit examples showing
the theoretical technique and the corresponding experimental procedure.Comment: 6 pages, 2 figure
Financing experimentation
Entrepreneurs must experiment to learn how good they are at a new activity. What happens when the experimentation is financed by a lender? Under common scenarios, i.e., when there is the opportunity to learn by "starting small" or when "noncompete" clauses cannot be enforced ex post, we show that financing experimentation can become harder precisely when it is more profitable, i.e., for lower values of the known arm and for more optimistic priors. Endogenous collateral requirements (like those frequently observed in micro-credit schemes) are shown to be part of the optimal contract
Multipartite entanglement in quantum algorithms
We investigate the entanglement features of the quantum states employed in
quantum algorithms. In particular, we analyse the multipartite entanglement
properties in the Deutsch-Jozsa, Grover and Simon algorithms. Our results show
that for these algorithms most instances involve multipartite entanglement
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