39 research outputs found
Can the wave function in configuration space be replaced by single-particle wave functions in physical space?
The ontology of Bohmian mechanics includes both the universal wave function
(living in 3N-dimensional configuration space) and particles (living in
ordinary 3-dimensional physical space). Proposals for understanding the
physical significance of the wave function in this theory have included the
idea of regarding it as a physically-real field in its 3N-dimensional space, as
well as the idea of regarding it as a law of nature. Here we introduce and
explore a third possibility in which the configuration space wave function is
simply eliminated -- replaced by a set of single-particle pilot-wave fields
living in ordinary physical space. Such a re-formulation of the Bohmian
pilot-wave theory can exactly reproduce the statistical predictions of ordinary
quantum theory. But this comes at the rather high ontological price of
introducing an infinite network of interacting potential fields (living in
3-dimensional space) which influence the particles' motion through the
pilot-wave fields. We thus introduce an alternative approach which aims at
achieving empirical adequacy (like that enjoyed by GRW type theories) with a
more modest ontological complexity, and provide some preliminary evidence for
optimism regarding the (once popular but prematurely-abandoned) program of
trying to replace the (philosophically puzzling) configuration space wave
function with a (totally unproblematic) set of fields in ordinary physical
space.Comment: 29 pages, 5 figures, to appear in Synthese Special Issue: Space-time
and the wave functio
How does Quantum Uncertainty Emerge from Deterministic Bohmian Mechanics?
Bohmian mechanics is a theory that provides a consistent explanation of
quantum phenomena in terms of point particles whose motion is guided by the
wave function. In this theory, the state of a system of particles is defined by
the actual positions of the particles and the wave function of the system; and
the state of the system evolves deterministically. Thus, the Bohmian state can
be compared with the state in classical mechanics, which is given by the
positions and momenta of all the particles, and which also evolves
deterministically. However, while in classical mechanics it is usually taken
for granted and considered unproblematic that the state is, at least in
principle, measurable, this is not the case in Bohmian mechanics. Due to the
linearity of the quantum dynamical laws, one essential component of the Bohmian
state, the wave function, is not directly measurable. Moreover, it turns out
that the measurement of the other component of the state -the positions of the
particles- must be mediated by the wave function; a fact that in turn implies
that the positions of the particles, though measurable, are constrained by
absolute uncertainty. This is the key to understanding how Bohmian mechanics,
despite being deterministic, can account for all quantum predictions, including
quantum randomness and uncertainty.Comment: To appear in Fluctuation and Noise Letters special issue "Quantum and
classical frontiers of noise
Multi‑scale simulations of two dimensional material based devices: the NanoTCAD ViDES suite
NanoTCAD ViDES (Versatile DEvice Simulator) is an open-source suite of computing codes aimed at assessing the operation
and the performance of nanoelectronic devices. It has served the computational nanoelectronic community for almost two
decades and it is freely available to researchers around the world in its website (http://vides.nanotcad.com), being employed
in hundreds of works by many electronic device simulation groups worldwide. We revise the code structure and its main
modules and we present the new features directed towards (i) multi-scale approaches exploiting ab-initio electron-structure
calculations, aiming at the exploitation of new physics in electronic devices, (ii) the inclusion of arbitrary heterostructures
of layered materials to devise original device architectures and operation, and (iii) the exploration of novel low-cost, green
technologies in the mesoscopic scale, as, e.g. printed electronics.Università di Pisa within
the CRUI-CAREERC PEP2D (contract No. 770047Italian Ministry of Education and Research (MIUR) in the framework
of the FoReLab project (Departments of Excellence
Electrically tunable lateral spin-valve transistor based on bilayer CrI3
The authors gratefully acknowledge Graphene Flagship Core 3 (Contract No. 881603). Work partially supported by the Italian Ministry of Education and Research (MIUR) in the framework of the FoReLab project (Departments of Excellence). The authors thank Efren Navarro-Moratalla for useful discussions.The online version contains supplementary material
available at https://doi.org/10.1038/s41699-023-00400-5.The recent discovery of two-dimensional (2D) magnetic materials has opened new frontiers for the design of nanoscale spintronic devices. Among 2D nano-magnets, bilayer CrI3 outstands for its antiferromagnetic interlayer coupling and its electrically-mediated magnetic state control. Here, leveraging on CrI3 magnetic and electrical properties, we propose a lateral spin-valve transistor based on bilayer CrI3, where the spin transport is fully controlled via an external electric field. The proposed proof-of-concept device, working in the ballistic regime, is able to both filter (>99%) and select ON/OFF the spin current up to a ratio of & AP;10(2), using a double split-gate architecture. Our results obtained exploiting a multiscale approach ranging from first-principles to out-of-equilibrium transport calculations, open unexplored paths towards the exploitation of bilayer CrI3 or related 2D nano-magnets, as a promising platform for future electrically tunable, compact, and scalable spintronic devices.Ministry of Education, Universities and Research (MIUR)
88160
CVD Graphene Contacts for Lateral Heterostructure MoS Field Effect Transistors
Intensive research is carried out on two-dimensional materials, in particular
molybdenum disulfide, towards high-performance transistors for integrated
circuits. Fabricating transistors with ohmic contacts is challenging due to the
high Schottky barrier that severely limits the transistors' performance.
Graphene-based heterostructures can be used in addition or as a substitute for
unsuitable metals. We present lateral heterostructure transistors made of
scalable chemical vapor-deposited molybdenum disulfide and chemical
vapor-deposited graphene with low contact resistances of about 9
k{\Omega}{\mu}m and high on/off current ratios of 10${^8}. We also present a
theoretical model calibrated on our experiments showing further potential for
scaling transistors and contact areas into the few nanometers range and the
possibility of a strong performance enhancement by means of layer optimizations
that would make transistors promising for use in future logic circuits.Comment: 23 page
Levothyroxine Monotherapy Cannot Guarantee Euthyroidism in All Athyreotic Patients
CONTEXT: Levothyroxine monotherapy is the treatment of choice for hypothyroid patients because peripheral T4 to T3 conversion is believed to account for the overall tissue requirement for thyroid hormones. However, there are indirect evidences that this may not be the case in all patients. OBJECTIVE: To evaluate in a large series of athyreotic patients whether levothyroxine monotherapy can normalize serum thyroid hormones and thyroid-pituitary feedback. DESIGN: Retrospective study. SETTING: Academic hospital. PATIENTS: 1,811 athyreotic patients with normal TSH levels under levothyroxine monotherapy and 3,875 euthyroid controls. MEASUREMENTS: TSH, FT4 and FT3 concentrations by immunoassays. RESULTS: FT4 levels were significantly higher and FT3 levels were significantly lower (p<0.001 in both cases) in levothyroxine-treated athyreotic patients than in matched euthyroid controls. Among the levothyroxine-treated patients 15.2% had lower serum FT3 and 7.2% had higher serum FT4 compared to euthyroid controls. A wide range of FT3/FT4 ratios indicated a major heterogeneity in the peripheral T3 production capacity in different individuals. The correlation between thyroid hormones and serum TSH levels indicated an abnormal feedback mechanism in levothyroxine-treated patients. CONCLUSIONS: Athyreotic patients have a highly heterogeneous T3 production capacity from orally administered levothyroxine. More than 20% of these patients, despite normal TSH levels, do not maintain FT3 or FT4 values in the reference range, reflecting the inadequacy of peripheral deiodination to compensate for the absent T3 secretion. The long-term effects of chronic tissue exposure to abnormal T3/T4 ratio are unknown but a sensitive marker of target organ response to thyroid hormones (serum TSH) suggests that this condition causes an abnormal pituitary response. A more physiological treatment than levothyroxine monotherapy may be required in some hypothyroid patients