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"Rho"ing a Cellular Boat with Rearward Membrane Flow.
The physicist Edward Purcell wrote in 1977 about mechanisms that cells could use to propel themselves in a low Reynolds number environment. Reporting in Developmental Cell, O'Neill et al. (2018) provide direct evidence for one of these mechanisms by optogenetically driving the migration of cells suspended in liquid through RhoA activation
Are All Particles Identical?
We consider the possibility that all particles in the world are fundamentally
identical, i.e., belong to the same species. Different masses, charges, spins,
flavors, or colors then merely correspond to different quantum states of the
same particle, just as spin-up and spin-down do. The implications of this
viewpoint can be best appreciated within Bohmian mechanics, a precise
formulation of quantum mechanics with particle trajectories. The implementation
of this viewpoint in such a theory leads to trajectories different from those
of the usual formulation, and thus to a version of Bohmian mechanics that is
inequivalent to, though arguably empirically indistinguishable from, the usual
one. The mathematical core of this viewpoint is however rather independent of
the detailed dynamical scheme Bohmian mechanics provides, and it amounts to the
assertion that the configuration space for N particles, even N
``distinguishable particles,'' is the set of all N-point subsets of physical
3-space.Comment: 12 pages LaTeX, no figure
Bell-Type Quantum Field Theories
In [Phys. Rep. 137, 49 (1986)] John S. Bell proposed how to associate
particle trajectories with a lattice quantum field theory, yielding what can be
regarded as a |Psi|^2-distributed Markov process on the appropriate
configuration space. A similar process can be defined in the continuum, for
more or less any regularized quantum field theory; such processes we call
Bell-type quantum field theories. We describe methods for explicitly
constructing these processes. These concern, in addition to the definition of
the Markov processes, the efficient calculation of jump rates, how to obtain
the process from the processes corresponding to the free and interaction
Hamiltonian alone, and how to obtain the free process from the free Hamiltonian
or, alternatively, from the one-particle process by a construction analogous to
"second quantization." As an example, we consider the process for a second
quantized Dirac field in an external electromagnetic field.Comment: 53 pages LaTeX, no figure
On the Role of Density Matrices in Bohmian Mechanics
It is well known that density matrices can be used in quantum mechanics to
represent the information available to an observer about either a system with a
random wave function (``statistical mixture'') or a system that is entangled
with another system (``reduced density matrix''). We point out another role,
previously unnoticed in the literature, that a density matrix can play: it can
be the ``conditional density matrix,'' conditional on the configuration of the
environment. A precise definition can be given in the context of Bohmian
mechanics, whereas orthodox quantum mechanics is too vague to allow a sharp
definition, except perhaps in special cases. In contrast to statistical and
reduced density matrices, forming the conditional density matrix involves no
averaging. In Bohmian mechanics with spin, the conditional density matrix
replaces the notion of conditional wave function, as the object with the same
dynamical significance as the wave function of a Bohmian system.Comment: 16 pages LaTeX, no figure
Strength of forelimb lateralization predicts motor errors in an insect
Lateralized behaviours are widespread in both vertebrates and invertebrates, suggesting that lateralization is advantageous. Yet evidence demonstrating proximate or ultimate advantages remains scarce, particularly in invertebrates or in species with individual-level lateralization. Desert locusts (Schistocerca gregaria) are biased in the forelimb they use to perform targeted reaching across a gap. The forelimb and strength of this bias differed among individuals, indicative of individual-level lateralization. Here we show that strongly biased locusts perform better during gap-crossing, making fewer errors with their preferred forelimb. The number of targeting errors locusts make negatively correlates with the strength of forelimb lateralization. This provides evidence that stronger lateralization confers an advantage in terms of improved motor control in an invertebrate with individual-level lateralization
Mitochondrial Function as a Potential Tool for Assessing Function, Quality and Adulteration in Medicinal Herbal Teas
Quality control has been a significant issue in herbal medicine since herbs became widely used to heal. Modern technologies have improved the methods of evaluating the quality of medicinal herbs but the methods of adulterating them have also grown in sophistication. In this paper we undertook a comprehensive literature search to identify the key analytical techniques used in the quality control of herbal medicine, reviewing their uses and limitations. We also present a new tool, based on mitochondrial profiling, that can be used to measure medicinal herbal quality. Besides being fundamental to the energy metabolism required for most cellular activities, mitochondria play a direct role in cellular signalling, apoptosis, stress responses, inflammation, cancer, ageing, and neurological function, mirroring some of the most common reasons people take herbal medicines. A fingerprint of the specific mitochondrial effects of medicinal herbs can be documented in order to assess their potential efficacy, detect adulterations that modulate these effects and determine the relative potency of batches. Furthermore, through this method it will be possible to assess whole herbs or complex formulas thus avoiding the issues inherent in identifying active ingredients which may be complex or unknown. Thus, while current analytical methods focus on determining the chemical quality of herbal medicines, including adulteration and contamination, mitochondrial functional analysis offers a new way of determining the quality of plant derived products that is more closely linked to the biological activity of a product and its potential clinical effectiveness
Trajectories and Particle Creation and Annihilation in Quantum Field Theory
We develop a theory based on Bohmian mechanics in which particle world lines
can begin and end. Such a theory provides a realist description of creation and
annihilation events and thus a further step towards a "beable-based"
formulation of quantum field theory, as opposed to the usual "observable-based"
formulation which is plagued by the conceptual difficulties--like the
measurement problem--of quantum mechanics.Comment: 11 pages LaTeX, no figures; v2: references added and update
Seven Steps Towards the Classical World
Classical physics is about real objects, like apples falling from trees,
whose motion is governed by Newtonian laws. In standard Quantum Mechanics only
the wave function or the results of measurements exist, and to answer the
question of how the classical world can be part of the quantum world is a
rather formidable task. However, this is not the case for Bohmian mechanics,
which, like classical mechanics, is a theory about real objects. In Bohmian
terms, the problem of the classical limit becomes very simple: when do the
Bohmian trajectories look Newtonian?Comment: 16 pages, LaTeX, uses latexsy
An Update on Grading of Salivary Gland Carcinomas
Histologic grade is a significant predictor of outcome in salivary gland carcinomas. However, the sheer variety of tumor type and the rarity of these tumors pose challenges to devising highly predictive grading schemes. As our knowledge base has evolved, it is clear that carcinoma ex pleomorphic adenoma is not automatically a high grade tumor as is traditionally suggested. These tumors should be further qualified as to type/grade of carcinoma and extent, since intracapsular and minimally invasive carcinomas ex pleomorphic adenoma behave favorably. The two carcinoma types for which grading schemes are common include adenoid cystic carcinoma and mucoepidermoid carcinoma. Adenoid cystic carcinomas are graded based solely on pattern with solid components portending a worse prognosis. Occasionally, adenoid cystic carcinomas may undergo transformation to pleomorphic high grade carcinomas. This feature confers a high propensity for lymph node metastasis and should thus be reported to alert the clinical team. Mucoepidermoid carcinomas are graded in a three tier fashion based on a constellation of features including cystic component, border, mitoses, anaplasia, and perineural invasion among others. All grading schemes are somewhat cumbersome, intimidating and occasionally ambiguous, but evidence suggests that using a scheme consistently shows greater reproducibility than using an intuitive approach. The intermediate grade category demonstrates the most variability between grading systems and thus the most controversy in management. In the AFIP system intermediate grade tumors cluster with high grade tumors, while in the Brandwein system, they cluster with low grade tumors
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