Overcoming a limitation of deterministic dense coding with a non-maximally entangled initial state

Under two-party deterministic dense-coding, Alice communicates (perfectly distinguishable) messages to Bob via a qudit from a pair of entangled qudits in pure state |Psi>. If |Psi> represents a maximally entangled state (i.e., each of its Schmidt coefficients is sqrt(1/d)), then Alice can convey to Bob one of d^2 distinct messages. If |Psi> is not maximally entangled, then Ji et al. [Phys. Rev. A 73, 034307 (2006)] have shown that under the original deterministic dense-coding protocol, in which messages are encoded by unitary operations performed on Alice's qudit, it is impossible to encode d^2-1 messages. Encoding d^2-2 is possible; see, e.g., the numerical studies by Mozes et al. [Phys. Rev. A 71, 012311 (2005)]. Answering a question raised by Wu et al. [Phys. Rev. A 73, 042311 (2006)], we show that when |Psi> is not maximally entangled, the communications limit of d^2-2 messages persists even when the requirement that Alice encode by unitary operations on her qudit is weakened to allow encoding by more general quantum operators. We then describe a dense-coding protocol that can overcome this limitation with high probability, assuming the largest Schmidt coefficient of |Psi> is sufficiently close to sqrt(1/d). In this protocol, d^2-2 of the messages are encoded via unitary operations on Alice's qudit, and the final (d^2-1)-th message is encoded via a (non-trace-preserving) quantum operation.Comment: 18 pages, published versio

Avian cerebellar floccular fossa size is not a proxy for flying ability in birds

Extinct animal behavior has often been inferred from qualitative assessments of relative brain region size in fossil endocranial casts. For instance, flight capability in pterosaurs and early birds has been inferred from the relative size of the cerebellar flocculus, which in life protrudes from the lateral surface of the cerebellum. A primary role of the flocculus is to integrate sensory information about head rotation and translation to stabilize visual gaze via the vestibulo-occular reflex (VOR). Because gaze stabilization is a critical aspect of flight, some authors have suggested that the flocculus is enlarged in flying species. Whether this can be further extended to a floccular expansion in highly maneuverable flying species or floccular reduction in flightless species is unknown. Here, we used micro computed-tomography to reconstruct “virtual” endocranial casts of 60 extant bird species, to extract the same level of anatomical information offered by fossils. Volumes of the floccular fossa and entire brain cavity were measured and these values correlated with four indices of flying behavior. Although a weak positive relationship was found between floccular fossa size and brachial index, no significant relationship was found between floccular fossa size and any other flight mode classification. These findings could be the result of the bony endocranium inaccurately reflecting the size of the neural flocculus, but might also reflect the importance of the flocculus for all modes of locomotion in birds. We therefore conclude that the relative size of the flocculus of endocranial casts is an unreliable predictor of locomotor behavior in extinct birds, and probably also pterosaurs and non-avian dinosaurs

Propylthiocyclopentadiene: A new synthetic route to complexes of iron and group 4 transition metals. Molecular structure of (C5H4SCH2CH2CH3)(2)ZrCl2

The use of the propylthio-substituted cyclopentadienylsodium salt leads to 1,1'-bis(propylthio) ferrocene and dichlorobis(propylthiocyclopentadienyl)zirconium, titanium or hafnium(IV). The structure of (C5H4SCH2CH2CH3)(2)ZrCl2 has been established by X-ray analysis (orthorhombic, Pbcn, a = 11.943(1) Angstrom, b = 6.883(2) Angstrom, c = 22.412(2) Angstrom, V = 1842.4(2) Angstrom(3), Z = 4, R(F) = 0.027). The complexes have been characterized by H-1 and C-13 NMR and electrochemical studies. The physico chemical properties of 1,1'-bis(propylthio) ferrocene are discussed by a molecular approach at the extended Huckel level

Melting of a Two-component Source beneath Iceland

New trace element and Hf-Nd isotope data on post-glacial basalts from Iceland's main rift zones are used in conjunction with literature data to evaluate the relative importance of source heterogeneity and the melting process for the final melt composition. Correlations between Hf and Nd isotope compositions and trace element ratios indicate that at least two source components are sampled systematically as a function of the degree and pressure of melting beneath Iceland. Strong depletion in Rb, Ba, U and Th and enrichment in Nb and Ta compared with La in the most enriched samples from the Reykjanes Peninsula and Western Rift Zone suggests that the enriched source component is similar to ancient recycled enriched mid-ocean ridge basalt (E-MORB) crust. Highly incompatible trace element ratios such as Nb/La and Nb/U and Pb isotope ratios are variable across Iceland. This observation suggests that either the enriched component is intrinsically heterogeneous, or that there is a larger proportion of the enriched source component beneath the Southwestern Rift Zone compared with the Northern Rift Zone. The relative effect of source heterogeneity and melting on the final melt composition was evaluated with a one-dimensional polybaric melt mixing model in which accumulated melts from a depleted MORB mantle and a recycled E-MORB crust are mixed in different ways. Two styles of melt mixing were simulated: (1) complete mixing of melts with variable proportions of the depleted mantle and recycled E-MORB components; (2) incomplete mixing with a fixed initial proportion of the two source components. Calculated pressure-dependent compositional changes using these simple two-component melting models can explain the observed trends in trace element ratio and isotope ratio diagrams for Icelandic basalts, even in cases where conventional binary mixing models would require more than two source components. The example of Iceland demonstrates that melt mixing during extraction from the mantle is a key process for controlling the trace element and isotope variability observed in basaltic lavas and must be evaluated before inferring the presence of multiple source component

τ→ρππν\tau\to\rho\pi\pi\nu decays

Effective chiral theory of mesons is applied to study the four decay modes of $\tau\to\rho\pi\pi\nu$. Theoretical values of the branching ratios are in agreement with the data. The theory predicts that the $a_{1}$ resonance plays a dominant role in these decays. There is no new parameter in this study.Comment: 12 pages and one figur

Electric field measurements in atmospheric-pressure plasma jets

Atmospheric pressure non-thermal plasmas are researched for many applications. They became popular with plasma medicine, where restrictions on the plasmas are rigorous - they have to be at room temperature and not transfer significant amount of charge to the target, while still providing a mixture of reactive species, charge, field, to be efficient in medical applications. The intended applications soon extended to the treatment of different types of targets, where it is either important to treat them at atmospheric pressure (e.g. water) or with a plasma at room temperature. Atomic layer deposition is a good example of a traditionally low pressure technology being extended into the atmospheric pressure, and so is plasma catalysis. Another family of applications is in food and agriculture, where plasmas present a promising technology applied to a wide range of surfaces, dielectrics of different permittivities, in atmospheric air but also in humid conditions.The discharges used in these developments very often belong to the family of non-thermal atmospheric pressure plasmas - these are transient discharges, highly non-uniform in both space and time, small-scale (sub-mm), low ionization level, low light output, and most importantly sensitive to their environment. For example, a He plasma jet working in a kHz bullet mode changes its properties when impinging on a target with respect to the case when it expands freely into the ambient atmosphere. This is an important aspect to be kept in mind when bringing non-thermal atmospheric pressure plasmas intoapplications. It is also the motivation for the research presented in this talk. This work focuses on the fundamental properties of non-thermal plasmas such as the electric field, charge density and electron temperature. The work was performed on a non-thermal atmospheric pressure He plasma jet working in a kHz-driven mode with one ionization wave produced per voltage period or pulse. These fundamental properties of the discharge were measured in a freely expanding jet as well as when impinging on targets of different types, from low-permittivity dielectrics such as glass, to water, to metal. The measurements were performed in the plasma plume, but also in a target when a high-permittivity dielectric (er = 56) was used.The results bring one of the first sets of data concerning the E field, electron density and electron temperature, which are relatable to each other through the fact that they were all obtained on the same discharge. The effect of the gas flow speed is significant in the freely expanding jet, showing that the increased flow extends not only the visible length of the plasma plume, but also its electric field profile. In addition, the electron density and temperature were shown to respectively fall and rise within the plasma plume with increasing the distance from the end of the glass capillary.The presence of the target influences the plasma plume in several different ways. For low-permittivity targets, such as plastic or glass, the presence of the target does not significantly influence the plasma properties in the plume, but it does initiate surface discharges belonging to the family of ionization waves. The electric field induced in the target material by those surface ionization waves were measured, both axially, in the direction through the material, and radially. When the permittivity of the target is increased, the surface ionization waves are replaced by one or several return strokes and a significantly altered electric field profile, along with increased electron density and temperature. In the extreme case of the metallic target, combined with much higher electron densities, the duration of the discharge on the metal surface is extended to a microsecond. The work shows not only that the presence of the target influences the plasma, but that the properties of the target determine the plasma parameters, also in the gas phase

Probing photo-ionization: simulations of positive streamers in varying N2:O2 mixtures

Photo-ionization is the accepted mechanism for the propagation of positive streamers in air though the parameters are not very well known; the efficiency of this mechanism largely depends on the presence of both nitrogen and oxygen. But experiments show that streamer propagation is amazingly robust against changes of the gas composition; even for pure nitrogen with impurity levels below 1 ppm streamers propagate essentially with the same velocity as in air, but their minimal diameter is smaller, and they branch more frequently. Additionally, they move more in a zigzag fashion and sometimes exhibit a feathery structure. In our simulations, we test the relative importance of photo-ionization and of the background ionization from pulsed repetitive discharges, in air as well as in nitrogen with 1 ppm O2 . We also test reasonable parameter changes of the photo-ionization model. We find that photo- ionization dominates streamer propagation in air for repetition frequencies of at least 1 kHz, while in nitrogen with 1 ppm O2 the effect of the repetition frequency has to be included above 1 Hz. Finally, we explain the feather-like structures around streamer channels that are observed in experiments in nitrogen with high purity, but not in air.Comment: 12 figure