El orden y la memoria en la Librería de Duportail Hermanos: un catálogo porteño de 1829 / Alejandro E. Parada. Buenos Aires: Instituto de Investigaciones Bibliotecológicas (INIBI), Facultad de Filosofía y Letras, Universidad de Buenos Aires, 2005. 192 p.

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Comment on “Phase contribution of image potential on empty quantum well states in Pb islands on the Cu(111) surface”

1 página, 1 figura.-- PACS numbers: 68.37.Ef, 68.65.Fg, 73.21.FgThis work was partially funded by MCINN(FIS2010- 19609-C02-01) and G.V-UPV/EHU(IT-366-07).Peer reviewe

Enhanced weak superconductivity in trigonal γ\gamma-PtBi2_2

Electrical transport experiments show superconductivity in a high-quality single crystal of trigonal $\gamma$-PtBi$_2$. The critical temperature shows a large dependence on the electrical current and in the limit of very low currents, a $T_c$ = 1.1 K is observed, while a zero temperature critical field $B_c$(0) $\approx$ 1.5 Tesla is estimated. These are the highest superconducting parameters reported (at ambient pressure) in a stoichiometric $\gamma$-PtBi$_2$ bulk sample so far. Under a magnetic field a strict zero resistance state is no longer observed even though an incipient superconducting transition is seen. Such a behavior is most probably associated with very low critical currents and is reminiscent of filamentary superconductivity. The superconducting state is elusive to magnetization measurements discarding a bulk phase down to $T =$ 0.3 K.Comment: 5 pages, 5 figure

Energetics of metal slabs and clusters: the rectangle-box model

An expansion of energy characteristics of wide thin slab of thickness L in power of 1/L is constructed using the free-electron approximation and the model of a potential well of finite depth. Accuracy of results in each order of the expansion is analyzed. Size dependences of the work function and electronic elastic force for Au and Na slabs are calculated. It is concluded that the work function of low-dimensional metal structure is always smaller that of semi-infinite metal sample. A mechanism for the Coulomb instability of charged metal clusters, different from Rayleigh's one, is discussed. The two-component model of a metallic cluster yields the different critical sizes depending on a kind of charging particles (electrons or ions). For the cuboid clusters, the electronic spectrum quantization is taken into account. The calculated critical sizes of Ag_{N}^{2-} and Au_{N}^{3-} clusters are in a good agreement with experimental data. A qualitative explanation is suggested for the Coulomb explosion of positively charged Na_{\N}^{n+} clusters at 3<n<5.Comment: 11 pages, 6 figures, 1 tabl

Excited states of Na nanoislands on the Cu(111) surface

Electronic states of one monolayer high Na nanoislands on the Cu(111) surface are studied as a function of the nanoisland size. Properties of nanoislands such as one-electron states, the electron density, and the associated potential are obtained self-consistently within the density-functional formalism using a one-dimensional pseudopotential for the Cu(111) substrate and the jellium model for Na. A wave packet propagation method is used to study the energies and lifetimes of quasistationary states localized at Na islands. For very large islands, island-localized states merge into the two-dimensional continuum of the Na quantum well state. Thus, we assign the quasistationary states studied as arising from the quantization of the two-dimensional quantum well continuum due to the finite island size. The scattering at the island boundaries results in the energy-conserving resonant electron transfer into the continuum of the substrate states broadening the island-localized states into resonances.Peer reviewe

Consumo voluntario, digestiblidad in vivo y selectividad en ovinos en función de distintas cantidades de agua agregada en dos especies forrajeras

Las gramíneas forrajeras perennes de crecimiento estival son un recurso de gran importancia para la ganadería pampeana. Panicum coloratum es una gramínea perenne de crecimiento estival que a comenzado a difundirse masivamente en la Región Semiárida Pampeana. Combinada con el "pasto llorón" (Eragrostis curvula (Schrad.) Nees) en los sistemas de cría, permitiría obtener un aumento en los índices de producción y de carga animal. Los verdeos de invierno son recursos forrajeros muy difundidos en los sistemas de invernada y tambo. Su utilidad responde básicamente a su excelente calidad y productividad, que los hace indispensables en muchas ocasiones, para proveer forraje durante el otoño, invierno y primavera. El objetivo de este estudio fue medir el consumo voluntario y la digestibilidad aparente in vivo de "mijo perenne" (Panicum coloratum) diferido y "triticale" (X Triticosecale) fresco y establecer patrones de comportamiento ingestivo ante diferentes cantidades de agua depositada en el forraje suministrado. Las mediciones se hicieron a galpón, con el empleo de 24 ovinos (Pampinta) machos castrados (PV: 34,96 ± 3,68 kg). En el primer estudio (El) se utilizó Panicum coloratum cv "Verde" diferido y en el segundo (E2) triticale (xTriticosecale) cv "Tehuelche", Los animales experimentales se distribuyen al azar en tres tratamientos: a) Testigo (T): forraje sin agregado de agua (E1:100,7 ± 1,0 g HP/kg MS; E2: 721,4 ± 41,2 g HPlkg MS); b) Intermedio (1): forraje más agregado de agua (E1: 276,6 ± 25,6 g H20/Kg MS; E2:731,3 ± 42,2 g HP/kg MS); e) Saturado (S): forraje con agua a saturación (El: 518,2 ± 39,7 g HP/kg MS; E2: 763,1 ± 36,6 g HP/ kg MS). El forraje fue cortado en forma manual a 5 cm de altura antes de cada uno de los dos suministros diarios (9:00 y 18:00 horas). Para obtener una distribución homogénea del agua en el forraje se utilizó una mochila para pulverizar, con lo que se logró un mojado total del mismo. Cada estudio tuvo siete días de toma de datos, previo período de acostumbramiento de trece días. Los CMS y CMSD (en g kg PV 0.75) fueron: E1; T: 51,52 ± 7,28 y 25,42 ± 3,64; I: 49,55 ± 7,14 y 23,93 ± 3,44; S: 43,79 ± 7,71 y 19,99 ± 6,93; respectivamente E2; T: 73,43 ± 5,00 y 51,78 ± 4,16; I: 81,70 ± 5,72 y 56,38 ± 7,74; S: 65,12 ± 8,25 y 42,36 ± 5,32. La DMS (en %) fue El; T: 49,60 ± 5,38; I: 52,63 ± 4,29; S: 44,68 ± 13,83. E2; T: 69,46 ± 1,93; 1: 69,06 ± 3,96; S: 65,08 ± 1,44. La PB (en %) fue El; Tallo: 1,64 ± 0,17; Lámina: 2,55 ± 0,32; T + L: 1,80 ± 0,10. E2; Tallo: 7,68 ± 2,28; Lámina: 14,30 ± 1,16; T + L: 9,24 ± 2,66. Con estos resultados concluimos que además del efecto de lluvia por sí misma, podría existir un efecto del agua adherida al forraje, siempre que ésta dificulte la selección que dentro del forraje ofrecido puedan realizar los animales. Por otra parte, se sugiere como práctica de manejo utilizar ambos forrajes para que los animales consuman una dieta balanceada.Director: Ing. Agr. Néstor Pedro Stritzler

Evaluation HPDC Lubricant Spraying for Improved Cooling and Die Protection

This study tries to find out a better cooling and temperature homogenization as well as better die protection on high-pressure die-casting (HPDC) spray lubrication. Test procedures have been set up to study the Leidenfrost point (LFP), contact angle (CA), film thickness and protection from die soldering of lubricants typically applied into the die surfaces during HPDC process. Five different lubricants have been studied as well as the influence in different controllable process parameters (type of die material, oxidation of the surface, temperature, roughness, droplet diameter, water hardness and lubricant concentration). The increase of the LFP, avoiding film boiling regime, and a reduced CA, improve the cooling and film ability of die surface during spraying. The best chemistry exhibits high LFP, shows an increased thickness of the formed film and is more effective preventing the sticking of the aluminum part to the die surface. Thermogravimetric analysis shows better thermal properties for lubricants with anti-sticking performance. The study performed and the test protocols set up result in a better insight of the involved phenomena and allow selecting the most favorable operating window for HPDC lubrication

Magnetic phenomena in 5d transition metal nanowires

We have carried out fully relativistic full-potential, spin-polarized, all-electron density-functional calculations for straight, monatomic nanowires of the 5d transition and noble metals Os, Ir, Pt and Au. We find that, of these metal nanowires, Os and Pt have mean-field magnetic moments for values of the bond length at equilibrium. In the case of Au and Ir, the wires need to be slightly stretched in order to spin polarize. An analysis of the band structures of the wires indicate that the superparamagnetic state that our calculations suggest will affect the conductance through the wires -- though not by a large amount -- at least in the absence of magnetic domain walls. It should thus lead to a characteristic temperature- and field dependent conductance, and may also cause a significant spin polarization of the transmitted current.Comment: 7 pages, 5 figure

The social wellbeing of irrigation water. A demand-side integrated valuation in a Mediterranean agroecosystem

[EN] Irrigation water is a vital input for agricultural production. The supply of irrigation water to crops enhances land productivity and affects the agroecosystem functioning. Agroecosystems co-provide a wide range of agroecosystem services and disservices, which contribute positively and negatively, respectively, to human wellbeing. Therefore, irrigated agroecosystems produce several positive and negative outcomes in relation to society, and agricultural water management is key to the provision of adequate incentives for the enhancement of social wellbeing. In such a context, the aim of this work was to value the contribution of water to the provision of agroecosystem services and disservices, as a way to summarise the contribution of irrigation to social wellbeing. To this end, a demand-side integrated valuation of agroecosystem services and disservices was carried out for both rain-fed and irrigated agriculture in two different agroecosystems of the Region of Murcia (south-eastern Spain), a semi-arid western Mediterranean region characterised by water scarcity. In addition, the intensity of the agricultural water use was considered by distinguishing traditional and highly-intensive irrigated agroecosystems. Almond and lemon, two woody crops, were employed to develop the economic valuation in rain-fed and irrigated agroecosystems, respectively. The assessment of biophysical indicators to quantify the provision of services and disservices and their economic valuation, using market and non-market methods, were used. The results show that the contribution of water to social wellbeing is valued at 9000-12,300 euro/ha/year, being greater when the intensive use of agricultural water is promoted. The net economic value of all categories of agroecosystem services and disservices increases when irrigation water is supplied. Notwithstanding, the greatest contribution is due to the increase in provisioning services, mainly food provision in the case of the highly-intensive agroecosystem. Traditional irrigated agroecosystems make a greater contribution to regulating and cultural agroecosystem services. Hence, agricultural water management should focus on increasing the contribution of irrigated agroecosystems to human wellbeing.This work was supported by the AgriCambio project (Grant PID2020- 114576RB-I00 funded by MCIN/AEI/ 10.13039/501100011033). Jos¿e A. Zabala, Víctor Martínez-García and Jos¿e A. Albaladejo-García acknowledge the financial support from the Spanish Ministry of Education and Personal Training (FPU 16/03473; FPU19/05143; FPU 16/ 03562)Alcon, F.; Zabala, J.; Matínez-García, V.; Albaladejo, J.; López-Becerra, E.; De Miguel, MD.; Martínez-Paz, JM. (2022). The social wellbeing of irrigation water. A demand-side integrated valuation in a Mediterranean agroecosystem. Agricultural Water Management. 262. https://doi.org/10.1016/j.agwat.2021.10740026

Quantum size effects in Pb islands on Cu(111): Electronic-structure calculations

The appearance of "magic" heights of Pb islands grown on Cu(111) is studied by self-consistent electronic structure calculations. The Cu(111) substrate is modeled with a one-dimensional pseudopotential reproducing the essential features, i.e. the band gap and the work function, of the Cu band structure in the [111] direction. Pb islands are presented as stabilized jellium overlayers. The experimental eigenenergies of the quantum well states confined in the Pb overlayer are well reproduced. The total energy oscillates as a continuous function of the overlayer thickness reflecting the electronic shell structure. The energies for completed Pb monolayers show a modulated oscillatory pattern reminiscent of the super-shell structure of clusters and nanowires. The energy minima correlate remarkably well with the measured most probable heights of Pb islands. The proper modeling of the substrate is crucial to set the quantitative agreement.Comment: 4 pages, 4 figures. Submitte