A D-dimensional Markovian open quantum system will undergo stochastic evolution which preserves pure states, if one monitors without loss of information the bath to which it is coupled. If a finite ...ensemble of pure states satisfies a particular set of constraint equations then it is possible to perform the monitoring in such a way that the (discontinuous) trajectory of the conditioned system state is, at all long times, restricted to those pure states. Finding these physically realisable ensembles (PREs) is typically very difficult, even numerically, when the system dimension is larger than 2. In this paper, we develop symmetry-based techniques that potentially greatly reduce the difficulty of finding a subset of all possible PREs. The two dynamical symmetries considered are an invariant subspace and a Wigner symmetry. An analysis of previously known PREs using the developed techniques provides us with new insights and lays the foundation for future studies of higher dimensional systems.
The effectiveness of monitoring and incentive alignment as mechanisms for controlling agency costs have been explored separately and in combination, with monitoring substituting for weaknesses in ...incentive alignment and vice versa; this equates to positive substitution when describing how monitoring and incentive alignment interact to influence shareholder agency costs. We draw upon behavioral agency theory and findings from finance research to offer further theoretical insight into how these mechanisms interact to influence agency costs. Our results suggest that CEO earnings management aimed at preserving their equity wealth (an incentive alignment mechanism) is accentuated by higher levels of concentrated institutional ownership, thereby imposing agency costs on less informed investors. Thus, in addition to being substitutes in controlling agency costs, as previously suggested, monitoring may accentuate the perverse effects of incentive alignment, equating to negative reinforcement, rather than positive substitution. Yet this effect is negated in the absence of CEO power due to dual occupation of the board and CEO roles. We discuss implications of these findings for theory and practice.
Currently, the concept of engineered tissues depends on the ability of cultured cells to fabricate new tissue around a scaffold. This is inherently slow and expensive and has had limited success so ...far. We report here a new process for the cell‐independent, controlled engineering of biomimetic scaffolds by rapid removal of fluid from hyperhydrated collagen gel (or other) constructs, using plastic compression (PC). PC fabrication produces dense, cellular, mechanically strong native collagen structures with controllable nano‐ and microscale biomimetic structures. The huge‐scale shrinkage (> 100‐fold) provides the ability to introduce controllable mechanical properties, microlayering, and embossed interface topography without cell participation, but with high cell viability. Critically, this takes minutes rather than the conventional days and weeks. The rapidity and biomimetic potential of the PC fabrication process at the mesoscale opens a new route for the production of biomaterials and patient‐customized tissues. It also represents a new concept in ‘engineering’ tissues.
Cell‐independent, controlled engineering of biomimetic scaffolds can be achieved by rapid fluid removal from hyperhydrated collagen gel via plastic compression. Mechanically strong native collagen with controllable nano‐ and microscale biomimetic structures (see Figure) can be produced over a timescale of minutes rather than the conventional days and weeks, providing promise for rapid production of biomaterials and patient‐customized tissues.
Ambient ionization methods for MS enable direct, high-throughput measurements of samples in the open air. Here, we report on one such method, desorption electrospray ionization (DESI), which is ...coupled to a linear ion trap mass spectrometer and used to record the spatial intensity distribution of a drug directly from histological sections of brain, lung, kidney, and testis without prior chemical treatment. DESI imaging provided identification and distribution of clozapine after an oral dose of 50 mg/kg by: i) measuring the abundance of the intact ion at m/z 327.1, and ii) monitoring the dissociation of the protonated drug compound at m/z 327.1 to its dominant product ion at m/z 270.1. In lung tissues, DESI imaging was performed in the full-scan mode over an m/z range of 200-1100, providing an opportunity for relative quantitation by using an endogenous lipid to normalize the signal response of clozapine. The presence of clozapine was detected in all tissue types, whereas the presence of the N-desmethyl metabolite was detected only in the lung sections. Quantitation of clozapine from the brain, lung, kidney, and testis, by using LC-MS/MS, revealed concentrations ranging from 0.05 μg/g (brain) to a high of 10.6 μg/g (lung). Comparisons of the results recorded by DESI with those by LC-MS/MS show good agreement and are favorable for the use of DESI imaging in drug and metabolite detection directly from biological tissues.
The Heisenberg limit to laser coherence C-the number of photons in the maximally populated mode of the laser beam-is the fourth power of the number of excitations inside the laser. We generalize the ...previous proof of this upper bound scaling by dropping the requirement that the beam photon statistics be Poissonian (i.e., Mandel's Q=0). We then show that the relation between C and sub-Poissonianity (Q<0) is win-win, not a tradeoff. For both regular (non-Markovian) pumping with semiunitary gain (which allows Q→-1), and random (Markovian) pumping with optimized gain, C is maximized when Q is minimized.
Caveolin-1 (Cav1) is a multifunctional scaffolding protein with multiple binding partners that is associated with cell surface caveolae and the regulation of lipid raft domains. Cav1 regulates ...multiple cancer-associated processes including cellular transformation, tumor growth, cell migration and metastasis, cell death and survival, multidrug resistance and angiogenesis. However, Cav1 has been reported to impact both positively and negatively on various aspects of tumor progression and while reported to function as a tumor suppressor, it has also been identified as a poor prognostic factor in various human cancers. In this review, we survey the functional roles of Cav1 in cancer and argue that Cav1 function is interdependent on tumor stage and the expression of molecular effectors that impact on its role during tumor progression.
A number of authors have suggested that nonlinear interactions can enhance resolution of phase shifts beyond the usual Heisenberg scaling of 1/n , where n is a measure of resources such as the number ...of subsystems of the probe state or the mean photon number of the probe state. These suggestions are based on calculations of “local precision” for particular nonlinear schemes. However, we show that there is no simple connection between the local precision and the average estimation error for these schemes, leading to a scaling puzzle. This puzzle is partially resolved by a careful analysis of iterative implementations of the suggested nonlinear schemes. However, it is shown that the suggested nonlinear schemes are still limited to an exponential scaling in n . (This scaling may be compared to the exponential scaling in n which is achievable if multiple passes are allowed, even for linear schemes.) The question of whether nonlinear schemes may have a scaling advantage in the presence of loss is left open. Our results are based on a new bound for average estimation error that depends on (i) an entropic measure of the degree to which the probe state can encode a reference phase value, called the G asymmetry, and (ii) any prior information about the phase shift. This bound is asymptotically stronger than bounds based on the variance of the phase-shift generator. The G asymmetry is also shown to directly bound the average information gained per estimate. Our results hold for any prior distribution of the shift parameter, and generalize to estimates of any shift generated by an operator with discrete eigenvalues.
We investigate whether quantum theory can be understood as the continuum limit of a mechanical theory, in which there is a huge, but finite, number of classical “worlds,” and quantum effects arise ...solely from a universal interaction between these worlds, without reference to any wave function. Here, a “world” means an entire universe with well-defined properties, determined by the classical configuration of its particles and fields. In our approach, each world evolves deterministically, probabilities arise due to ignorance as to which world a given observer occupies, and we argue that in the limit of infinitely many worlds the wave function can be recovered (as a secondary object) from the motion of these worlds. We introduce a simple model of such a “many interacting worlds” approach and show that it can reproduce some generic quantum phenomena—such as Ehrenfest’s theorem, wave packet spreading, barrier tunneling, and zero-point energy—as a direct consequence of mutual repulsion between worlds. Finally, we perform numerical simulations using our approach. We demonstrate, first, that it can be used to calculate quantum ground states, and second, that it is capable of reproducing, at least qualitatively, the double-slit interference phenomenon.
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