204 research outputs found
Ciencia y sociedad civil
This paper analyses the relationship between scientific knowledge and the societies in which it is produced. After considering the diverse societal roles science has performed in different types of society, the discussion focuses on science’s role in democratic and pluralistic societies. Opposite to the increasing instrumental role knowledge production plays nowadays, for which it has been named «post-academic science» or «technoscience», non instrumental roles of traditional academic research are defended. It is argued that only if academic science keeps its autonomy and integrity from political and corporate interests, it may serve civil society by offering impartial and trustworthy knowledge to balance biases produced by the features of post-academic science.En este artículo se analizan las relaciones del conocimiento científico con las sociedades en las que se produce. Tras repasar sus diversas funciones en tipos distintos de sociedades, la discusión se centra en los fines de la ciencia en las sociedades democráticas pluralistas. Frente al cada vez mayor rol instrumental de la ciencia, por el que ha recibido los nombres de «ciencia postacadémica» o «tecnociencia», se defienden los roles no instrumentales tradicionales de la investigación académica clásica. Se argumenta que sólo si la ciencia académica mantiene su autonomía y su integridad frente a intereses políticos o empresariales podrá ser de utilidad al público al ofrecerle conocimiento imparcial y fidedigno frente a los sesgos producidos por la naturaleza propia de la ciencia postacadémica
Spin-Hall transport of heavy holes in III-V semiconductor quantum wells
We investigate spin transport of heavy holes in III-V semiconductor quantum
wells in the presence of spin-orbit coupling of the Rashba type due to
structure-inversion asymmetry. Similarly to the case of electrons, the
longitudinal spin conductivity vanishes, whereas the off-diagonal elements of
the spin-conductivity tensor are finite giving rise to an intrinsic spin-Hall
effect. For a clean system we find a closed expression for the spin-Hall
conductivity depending on the length scale of the Rashba coupling and the hole
density. In this limit the spin-Hall conductivity is enhanced compared to its
value for electron systems, and it vanishes with increasing strength of the
impurity scattering. As an aside, we also derive explicit expressions for the
Fermi momenta and the densities of holes in the different dispersion branches
as a function of the spin-orbit coupling parameter and the total hole density.
These results are of relevance for the interpretation of possible Shubnikov-de
Haas measurements detecting the Rashba spin splitting.Comment: 6 pages, 2 figures included, some prefactor corrected, version to be
published in Phys. Rev.
Infrared Hall angle in the d-density-wave state: A comparison of theory and experiment
Infrared Hall measurements in the pseudogap phase of the high-T-c cuprates are addressed within the framework of the ordered d-density-wave state. The zero-temperature Hall frequency omega(H) is computed as a function of the hole-doping x. Our results are consistent with recent experiments in absolute units. We also discuss the signature of the quantum critical point in the Hall frequency at a critical doping inside the superconducting dome, which can be tested in future experiments
A tunable amorphous p-type ternary oxide system:the highly mismatched alloy of copper tin oxide
The approach of combining two mismatched materials to form an amorphous alloy was used to synthesise ternary oxides of CuO and SnO2. These materials were analysed across a range of compositions, and the electronic structure was modelled using density functional theory. In contrast to the gradual reduction in optical band gap, the films show a sharp reduction in both transparency and electrical resistivity with copper contents greater than 50%. Simulations indicate that this change is caused by a transition from a dominant Sn 5s to Cu 3d contribution to the upper valence band. A corresponding decrease in energetic disorder results in increased charge percolation pathways: a “compositional mobility edge.” Contributions from Cu(II) sub band-gap states are responsible for the reduction in optical transparency
Optical properties of quantum wires: Disorder-scattering in the Lloyd-model
The Lloyd model is extended to the exciton problem in quasi one-dimensional
structures to study the interplay between the Coulomb attraction and disorder
scattering. Within this model the averaging and resummation of the locator
series can be performed analytically. As an application, the optical absorption
in quantum box wires is investigated. Without electron-hole interaction,
fluctuations in the well-width lead to an asymmetric broadening of the
minibands with respect to the lower and upper band-edges.Comment: 7 pages, 6 figure
Bosonic Excitations in Random Media
We consider classical normal modes and non-interacting bosonic excitations in
disordered systems. We emphasise generic aspects of such problems and parallels
with disordered, non-interacting systems of fermions, and discuss in particular
the relevance for bosonic excitations of symmetry classes known in the
fermionic context. We also stress important differences between bosonic and
fermionic problems. One of these follows from the fact that ground state
stability of a system requires all bosonic excitation energy levels to be
positive, while stability in systems of non-interacting fermions is ensured by
the exclusion principle, whatever the single-particle energies. As a
consequence, simple models of uncorrelated disorder are less useful for bosonic
systems than for fermionic ones, and it is generally important to study the
excitation spectrum in conjunction with the problem of constructing a
disorder-dependent ground state: we show how a mapping to an operator with
chiral symmetry provides a useful tool for doing this. A second difference
involves the distinction for bosonic systems between excitations which are
Goldstone modes and those which are not. In the case of Goldstone modes we
review established results illustrating the fact that disorder decouples from
excitations in the low frequency limit, above a critical dimension , which
in different circumstances takes the values and . For bosonic
excitations which are not Goldstone modes, we argue that an excitation density
varying with frequency as is a universal
feature in systems with ground states that depend on the disorder realisation.
We illustrate our conclusions with extensive analytical and some numerical
calculations for a variety of models in one dimension
Practical Applications as a Source of Credibility: A Comparison of Three Fields of Dutch Academic Chemistry
In many Western science systems, funding structures increasingly stimulate academic research to contribute to practical applications, but at the same time the rise of bibliometric performance assessments have strengthened the pressure on academics to conduct excellent basic research that can be published in scholarly literature. We analyze the interplay between these two developments in a set of three case studies of fields of chemistry in the Netherlands. First, we describe how the conditions under which academic chemists work have changed since 1975. Second, we investigate whether practical applications have become a source of credibility for individual researchers. Indeed, this turns out to be the case in catalysis, where connecting with industrial applications helps in many steps of the credibility cycle. Practical applications yield much less credibility in environmental chemistry, where application-oriented research agendas help to acquire funding, but not to publish prestigious papers or to earn peer recognition. In biochemistry practical applications hardly help in gaining credibility, as this field is still strongly oriented at fundamental questions. The differences between the fields can be explained by the presence or absence of powerful upstream end-users, who can afford to invest in academic research with promising long term benefits
Of false promises and good bets: a plea for a pragmatic approach to theory building (the Tartu lecture)
Normal Accidents of Expertise
Charles Perrow used the term “normal accidents” to characterize a type of catastrophic failure that resulted when complex, tightly coupled production systems encountered a certain kind of anomalous event. These were events in which systems failures interacted with one another in a way that could not be anticipated, and could not be easily understood and corrected. Systems of the production of expert knowledge are increasingly becoming tightly coupled. Unlike classical science, which operated with a long time horizon, many current forms of expert knowledge are directed at immediate solutions to complex problems. These are prone to breakdowns like the kind discussed by Perrow. The example of the Homestake mine experiment shows that even in modern physics complex systems can produce knowledge failures that last for decades. The concept of knowledge risk is introduced, and used to characterize the risk of failure in such systems of knowledge production
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