Observation of zero-point quantum fluctuations of a single-molecule magnet through the relaxation of its nuclear spin bath

A single-molecule magnet placed in a magnetic field perpendicular to its anisotropy axis can be truncated to an effective two-level system, with easily tunable energy splitting. The quantum coherence of the molecular spin is largely determined by the dynamics of the surrounding nuclear spin bath. Here we report the measurement of the nuclear spin--lattice relaxation in a single crystal of the single-molecule magnet Mn$_{12}$-ac, at $T \approx 30$ mK in perpendicular fields $B_{\perp}$ up to 9 T. Although the molecular spin is in its ground state, we observe an increase of the nuclear relaxation rates by several orders of magnitude up to the highest $B_{\perp}$. This unique finding is a consequence of the zero-point quantum fluctuations of the Mn$_{12}$-ac spin, which allow it to efficiently transfer energy from the excited nuclear spin bath to the lattice. Our experiment highlights the importance of quantum fluctuations in the interaction between an `effective two-level system' and its surrounding spin bath.Comment: 5 pages, 4 figure

A Comparison of Agricultural Productivity in the European Union Regions

This paper is concerned with the estimation of productivity and technical progress based on DEA applied to complete panel data (intertemporal-DEA). Instead of assuming unchanged technology, this paper presents a formulation of technical change that allows the decomposition of productivity scores obtained using intertemporal-DEA. The assumption here is that the technology level in period t for each country is the maximum productivity index obtained until this period. The model assumes that improvements over earlier productivity levels are due to technical progress and that productivity scores below the earlier maximum productivity level are due to inefficiency. The methodology is applied to the analysis of agricultural productivity in the European Union regions in the 1985-97 period. The major source of data is Cronos in Eurostat. This database is used to obtain the disaggregated outputs, intermediate inputs, and depreciation, in current and constant 1990 prices, and labor in annual work units. Capital is measured by depreciation. Land is agricultural area in hectares. Outputs are aggregated in two categories: crops and animal products. Intermediate inputs are grouped into two major categories: feedstuffs and other materials. Aggregation uses national price indices and regional production structures, using the translog price formula. All output, intermediate input and depreciation data, originally reported in local currencies was converted into ECUs, using the 1990 exchange rates. The discriminatory power of the analysis is higher than those with only contemporary analysis of technical efficiency, giving less than 10% of observations in the reference set. Further discrimination is explored using super-efficiency analysis. Radial efficiency measures give only a particular form of inefficiency that can be explained by a proportional contraction in input usage. The paper studies particular output and input efficiencies. As examples, animal products inefficiency is usual only in southern regions. Inefficiency in intermediate consumption usage is pervasive, suggesting the possibility of reducing agricultural production costs. Labor and capital inefficiencies arise in different regions. Land slacks are common in the southern and the westernmost regions.

Complex-linear invariants of biochemical networks

The nonlinearities found in molecular networks usually prevent mathematical analysis of network behaviour, which has largely been studied by numerical simulation. This can lead to difficult problems of parameter determination. However, molecular networks give rise, through mass-action kinetics, to polynomial dynamical systems, whose steady states are zeros of a set of polynomial equations. These equations may be analysed by algebraic methods, in which parameters are treated as symbolic expressions whose numerical values do not have to be known in advance. For instance, an "invariant" of a network is a polynomial expression on selected state variables that vanishes in any steady state. Invariants have been found that encode key network properties and that discriminate between different network structures. Although invariants may be calculated by computational algebraic methods, such as Gr\"obner bases, these become computationally infeasible for biologically realistic networks. Here, we exploit Chemical Reaction Network Theory (CRNT) to develop an efficient procedure for calculating invariants that are linear combinations of "complexes", or the monomials coming from mass action. We show how this procedure can be used in proving earlier results of Horn and Jackson and of Shinar and Feinberg for networks of deficiency at most one. We then apply our method to enzyme bifunctionality, including the bacterial EnvZ/OmpR osmolarity regulator and the mammalian 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase glycolytic regulator, whose networks have deficiencies up to four. We show that bifunctionality leads to different forms of concentration control that are robust to changes in initial conditions or total amounts. Finally, we outline a systematic procedure for using complex-linear invariants to analyse molecular networks of any deficiency.Comment: 36 pages, 6 figure

Las dimensiones morales del interés por la verdad

This unpublished work is the written version of a paper presented to philosophy teachers which develops some of the ideas of his work 'El interés por la verdad'. According to Millán-Puelles’ view, our interest in truth is twofold: cognitive and communicative. This paper deals with the first of these two interests, our interest in truth, and in particular some of its moral aspects

Is Lactate an Oncometabolite? Evidence Supporting a Role for Lactate in the Regulation of Transcriptional Activity of Cancer-Related Genes in MCF7 Breast Cancer Cells.

Lactate is a ubiquitous molecule in cancer. In this exploratory study, our aim was to test the hypothesis that lactate could function as an oncometabolite by evaluating whether lactate exposure modifies the expression of oncogenes, or genes encoding transcription factors, cell division, and cell proliferation in MCF7 cells, a human breast cancer cell line. Gene transcription was compared between MCF7 cells incubated in (a) glucose/glutamine-free media (control), (b) glucose-containing media to stimulate endogenous lactate production (replicating some of the original Warburg studies), and (c) glucose-containing media supplemented with L-lactate (10 and 20 mM). We found that both endogenous, glucose-derived lactate and exogenous, lactate supplementation significantly affected the transcription of key oncogenes (MYC, RAS, and PI3KCA), transcription factors (HIF1A and E2F1), tumor suppressors (BRCA1, BRCA2) as well as cell cycle and proliferation genes involved in breast cancer (AKT1, ATM, CCND1, CDK4, CDKN1A, CDK2B) (0.001 < p < 0.05 for all genes). Our findings support the hypothesis that lactate acts as an oncometabolite in MCF7 cells. Further research is necessary on other cell lines and biopsy cultures to show generality of the findings and reveal the mechanisms by which dysregulated lactate metabolism could act as an oncometabolite in carcinogenesis

Decide to Digitalize! Barriers, Drivers and the Entrepreneurial Cognition Perspective

This article introduces the special issue Decide to Digitalize! Barriers, Drivers and the Entrepreneurial Cognition Perspective. Nine research papers have been selected to reach two primary research aims: first, to understand how entrepreneurs, cognitively, make strategical decisions in order to be more competitive in the technology sector; second, to investigate how digital technologies and ICTs are being used in the context of SMEs and entrepreneurshi

Experimental analysis of thermal storage tank configurationin a solar cooling installation with an absorption chiller

The use of air conditioning systems in Spanish dwellings is gaining popularity, as the installed units grows by 0,8 million per year. The most popular air conditioning system today is the vapor-compression cycle. This kind of system consumes a considerable amount of electric energy as it incorporates a mechanical compressor in its cycle and utilizes refrigerants that can be dangerous to the environment. A solution to this kind of equipment can be found in Solar Facilities configured to produce cold water for air conditioning purposes by means of an absorption chiller. This kind of equipment can be driven by a heat input produced by the solar facility. This machine consumes a very low amount of electric energy and presents great advantages for the environment. Nevertheless, the need of a heat reservoir to operate in the afternoon hours, where solar radiation is not enough to drive the chiller, is indispensable in a solar facility. To serve this purpose, the introduction of a thermal storage tank has to be made. There are two basic internal configurations of a thermal storage tank in a solar cooling facility. These are Stratification and Well-mixed configuration. Experimental results show that for solar cooling applications, having a homogeneous mixture temperature in the thermal storage tank produce more daily cooling energy than in an stratified one, although the solar field efficiency is lower. This gives the facility more autonomy of operation in the afternoon, when the sun goes down and radiation is not enough for the application. Effects on the facility produced by Well-mixed configuration are: efficiency reduction on the solar collector’s field , 0,27, higher daily COP’s, 0,33, and extended solar cooling time of about two hours.Universidad Carlos III de Madrid - ITEA Research GroupPublicad