Noninvasiveness and time symmetry of weak measurements

Measurements in classical and quantum physics are described in fundamentally different ways. Nevertheless, one can formally define similar measurement procedures with respect to the disturbance they cause. Obviously, strong measurements, both classical and quantum, are invasive -- they disturb the measured system. We show that it is possible to define general weak measurements, which are noninvasive: the disturbance becomes negligible as the measurement strength goes to zero. Classical intuition suggests that noninvasive measurements should be time symmetric (if the system dynamics is reversible) and we confirm that correlations are time-reversal symmetric in the classical case. However, quantum weak measurements -- defined analogously to their classical counterparts -- can be noninvasive but not time symmetric. We present a simple example of measurements on a two-level system which violates time symmetry and propose an experiment with quantum dots to measure the time-symmetry violation in a third-order current correlation function.Comment: 19 pages, 5 figures, more information at http://www.fuw.edu.pl/~abednorz/tasym

Alkoxylated β-Naphthol as an Additive for Tin Plating from Chloride and Methane Sulfonic Acid Electrolytes

Beta-naphthol was one of the first additives introduced for smooth and homogeneoustin electrodeposition. Although it can be oxidized under the plating conditions, forming either1,2-napthoquinone or polymeric materials based on naphthioxides, it is still in use. In this work,an investigation of its more stable form, alkoxylated beta-naphthol (ABN), on tin plating is undertaken.For this purpose, chloride based (pH ~5) and methane sulfonic acid (MSA, pH ~0.5) electrolytes,including ABN, were prepared. Reaction kinetics were studied by polarization, Tafel measurements,and cyclic voltammetry. Tin electrodeposits were obtained on flat brass substrates. Surfacemorphology and preferred crystal orientation were studied by Scanning Electron Microscopy (SEM)and X-ray Diffraction (XRD). In both studied electrolytes ABN acts as an inhibitor but in the case ofthe chloride electrolyte it is more pronounced. In the MSA electrolyte this effect was overlaid by thepresence of tin-citrate complexes. In the chloride-based electrolyte, ABN has a grain refining effect,while in the MSA electrolyte an increase of ABN concentration leads to a slight enlargement of theaverage grain size. X-ray analysis shows a constant decrease of the (101) intensity with increasingconcentration of ABN for the sample deposited from both baths

The Magellania venosa Biomineralizing Proteome: A Window into Brachiopod Shell Evolution

Brachiopods are a lineage of invertebrates well known for the breadth and depth of their fossil record. Although the quality of this fossil record attracts the attention of paleontologists, geochemists, and paleoclimatologists, modern day brachiopods are also of interest to evolutionary biologists due to their potential to address a variety of questions ranging from developmental biology to biomineralization. The brachiopod shell is a composite material primarily composed of either calcite or calcium phosphate in close association with proteins and polysaccharides which give these composite structures their material properties. The information content of these biomolecules, sequestered within the shell during its construction, has the potential to inform hypotheses focused on describing how brachiopod shell formation evolved. Here, using high throughput proteomic approaches and next generation sequencing, we have surveyed and characterized the first shell-proteome and shell-forming transcriptome of any brachiopod, the South American Magellania venosa (Rhynchonelliformea: Terebratulida). We find that the seven most abundant proteins present in the shell are unique to M. venosa, but that these proteins display biochemical features found in other metazoan biomineralization proteins. We can also detect some M. venosa proteins that display significant sequence similarity to other metazoan biomineralization proteins, suggesting that some elements of the brachiopod shell-forming proteome are deeply evolutionarily conserved. We also employed a variety of preparation methods to isolate shell proteins and find that in comparison to the shells of other spiralian invertebrates (such as mollusks) the shell ultrastructure of M. venosa may explain the effects these preparation strategies have on our results