High-performance aromatic polyamides García, José M.; García, Félix C.; Serna, Felipe ...
Progress in polymer science,
05/2010, Letnik:
35, Številka:
5
Journal Article
Recenzirano
Wholly aromatic polyamides (aramids) are considered to be high-performance organic materials due to their outstanding thermal and mechanical resistance. Their properties arise from their aromatic ...structure and amide linkages, which result in stiff rod-like macromolecular chains that interact with each other via strong and highly directional hydrogen bonds. These bonds create effective crystalline microdomains, resulting in a high-level intermolecular packing and cohesive energy. The better known commercial aramids, poly(
p-phenylene terephthalamide) and poly(
m-phenylene isophthalamide), are used in advanced technologies and have been transformed into high-strength and flame resistant fibers and coatings, with applications in the aerospace and armament industry, bullet-proof body armor, protective clothing, sport fabrics, electrical insulation, asbestos substitutes, and industrial filters, among others. Owing to their chemical structure, they exhibit extremely high transition temperatures that lie above their decomposition temperatures, are sparingly soluble in common organic solvents and, accordingly, can only be transformed upon solution. Research efforts are therefore underway to take advantage of their properties, enhance their processability and solubility, and incorporate new chemical functionalities in the polyamide backbone or lateral structure, so that their applicability is expanded and remains on the forefront of scientific research.
Canonical quantization has conventionally been adopted as a necessary procedure for the description of the quantum radiation field by analogy between quantum-mechanical oscillators and field ...oscillators. In this paper we provide the physical basis for the formal quantization of the radiation field interacting with matter in the presence of the vacuum field, taken here as a solution of classical Maxwell equations. Just as the canonical particle operators
x
^
,
p
^
have been shown to be the response functions of the particle to this field, here we derive the creation and annihilation operators
a
^
†
,
a
^
, with
a
^
,
a
^
†
=
1
, as an expression of the field’s response to this interaction. The results obtained shed new light on the physical meaning of the description of light in terms of operators and suggest that neither matter nor radiation are quantized in isolation.
How fast is a quantum jump? de la Peña, L.; Cetto, A.M.; Valdés-Hernández, A.
Physics letters. A,
12/2020, Letnik:
384, Številka:
34
Journal Article
Recenzirano
Odprti dostop
•We propose a way to estimate the duration of a single atomic transition.•The action of the zero-point field of Compton's frequency on the electron is central.•Our theoretical result is expressed in ...terms of universal constants.•The estimated time is on the order of attoseconds, in line with recent experiments.
A proposal is put forward for an estimate of the duration of a transition between atomic states. The proposal rests on the consideration that a resonance of the atomic electron with modes of the zero-point radiation field of Compton's frequency is at the core of the phenomenon. The theoretical result, given essentially by the expression (αωC)−1, where α is the fine structure constant and ωC the Compton angular frequency for the electron, lies well within the range of the recently experimentally estimated values of the order of attoseconds (10−18 s).
The theories of stochastic quantum mechanics and stochastic electrodynamics bring to light important aspects of the quantum dynamics that are concealed in the standard formalism. Here, we take ...further previous work regarding the connection between the two theories, to exhibit the role of stochasticity and diffusion in the process leading from the originally
classical
+
zpf
regime
to the
quantum regime
. Quantumlike phenomena present in other instances in which a mechanical system is subject to an appropriate oscillating background that introduces stochasticity, may point to a more general appearance of quantization under such circumstances.
In recent years weak values have been used to explore interesting quantum features in novel ways. In particular, the real part of the weak value of the momentum operator has been widely studied, ...mainly in connection with Bohmian trajectories. Here we focus on the imaginary part and its role in relation with the entanglement of a bipartite system. We establish an entanglement criterion based on weak momentum correlations, that allows to discern whether the entanglement is encoded in the amplitude and/or in the phase of the wave function. Our results throw light on the physical role of the real and imaginary parts of the weak values, and stress the relevance of the latter in the multi-particle scenario.
•The imaginary part of the weak value of the momentum is related to characteristic quantum features.•In bipartite systems it becomes relevant in certifying the entanglement of the state.•Weak values unveil entanglement in the amplitude or in the phase of the wave function independently.•Weak correlations of observables provide novel entanglement criteria in continuous variable systems.
This paper describes a strategy followed to achieve a sensing phenomenon in aqueous media using water-insoluble organic molecules. A sensory polymeric material for the colorimetric sensing of cyanide ...in water has been developed based on the reactivity of this anion with a fluorene derivative.
This hypothesis-generating trial evaluated neoadjuvant ipatasertib–paclitaxel for early triple-negative breast cancer (TNBC).
In this randomized phase II trial, patients with early TNBC (T≥1.5cm, ...N0–2) were randomized 1:1 to receive weekly paclitaxel 80mg/m2 with ipatasertib 400mg or placebo (days 1–21 every 28days) for 12weeks before surgery. Co-primary end points were pathologic complete response (pCR) rate (ypT0/TisN0) in the intention-to-treat (ITT) and immunohistochemistry phosphatase and tensin homolog (PTEN)-low populations. Secondary end points included pCR rate in patients with PIK3CA/AKT1/PTEN-altered tumors and pre-surgery response rates by magnetic resonance imaging (MRI).
pCR rates with ipatasertib versus placebo were 17% versus 13%, respectively, in the ITT population (N=151), 16% versus 13% in the immunohistochemistry PTEN-low population (N=35), and 18% versus 12% in the PIK3CA/AKT1/PTEN-altered subgroup (N=62). Rates of overall and complete response (CR) by MRI favored ipatasertib in all three populations (CR rate 39% versus 9% in the PIK3CA/AKT1/PTEN-altered subgroup). Ipatasertib was associated with more grade ≥3 adverse events (32% versus 16% with placebo), especially diarrhea (17% versus 1%). Higher cycle 1 day 8 (C1D8) immune score was significantly associated with better response only in placebo-treated patients. All ipatasertib-treated patients with low immune scores and a CR had PIK3CA/AKT1/PTEN-altered tumors.
Adding ipatasertib to 12weeks of paclitaxel for early TNBC did not clinically or statistically significantly increase pCR rate, although overall response rate by MRI was numerically higher with ipatasertib. The antitumor effect of ipatasertib was most pronounced in biomarker-selected patients. Safety was consistent with prior experience of ipatasertib–paclitaxel. A T-cell-rich environment at C1D8 had a stronger association with improved outcomes in paclitaxel-treated patients than seen for baseline tumor-infiltrating lymphocytes. This dependency may be overcome with the addition of AKT inhibition, especially in patients with PIK3CA/AKT1/PTEN-altered tumors.
NCT02301988.
The problem of a charged particle enclosed in an infinite square potential well is analysed from the point of view of classical theory with the addition of the electromagnetic zero-point radiation ...field, with the aim to explore the extent to which such an analysis can contribute to enhance our understanding of the quantum behavior. First a proper treatment is made of the freely moving particle subject to the action of the radiation field, involving a frequency cutoff
ω
c
. The jittering motion and the effective structure of the particle are sustained by the permanent action of the zero-point field. As a result, the particle interacts resonantly with the traveling field modes of frequency
ω
c
in its proper frame of reference, which superpose to give rise to a modulated wave accompanying the particle. This is identified with the de Broglie wave, validating the choice of Compton’s frequency for
ω
c
. For the stationary states of particles confined in the potential well, the Lorentz force produced by the accompanying field is shown to lead to discrete values for the mean speed and to an uneven probability distribution that echoes the corresponding quantum distribution. The relevance of the results obtained and the limitations of the classical approach used, are discussed in the context of present-day stochastic electrodynamics.
The introduction of host units, also called binding sites or receptor subunits, and fluorescence or chromogenic signaling motifs into the lateral or into the main polymer chain opens the way for ...cutting-edge applications related to the selective interaction of these chemical sites with guest or target molecules (i.e., cations, anions or neutral molecules). Thus, the good mechanical properties of these polymers permit the design and preparation of "á la carte" fluorogenic or colorimetric probes for sensing diverse analytes. These polymeric probes may work in organic or aqueous solutions and, most importantly, in the solid state, as finished materials, can operate in aqueous media, permitting the preparation of "naked-eye" solid probes to be used by non-specialist personnel, for example, to control the concentration of analytes in chemical industries or to test whether environmental polluting chemicals exceed the legal limits.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
We offer a clear physical explanation for the emergence of the quantum operator formalism, by revisiting the role of the vacuum field in quantum mechanics. The vacuum or random zero-point radiation ...field has been shown previously—using the tools of stochastic electrodynamics—to be central in allowing a particle subject to a conservative binding force to reach a stationary state of motion. Here we focus on the stationary states, and consider the role of the vacuum as a
driving force
. We observe that the particle responds resonantly to certain modes of the field. A proper Hamiltonian analysis of this response allows us to unequivocally trace the origin of the basic quantum commutator,
x
,
p
=
i
ħ
, by establishing a one-to-one correspondence between the response coefficients of
x
and
p
and the respective matrix elements. The (random) driving field variables disappear thus from the description, but their Hamiltonian properties become embodied in the operator formalism. The Heisenberg equations establish the dynamical relationship between the response functions.
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