Electrochemically induced nanocluster migration

In the presented study the influence of electrochemical treatments on size-selected Pt nanoclusters (NCs) supported on amorphous carbon is investigated by means of transmission electron microscopy (TEM). Well-defined Pt NCs are prepared by an ultra-high vacuum (UHV) laser vaporization source and deposited with low kinetic energy (≤10 eV/cluster) onto TEM gold grids covered by a thin (2 nm) carbon film. After transfer out of UHV Pt NCs are verified to be uniform in size and randomly distributed on the support. Subsequently, the TEM grids are employed as working electrodes in a standard electrochemical three electrode setup and the Pt nanoclusters are subjected to different electrochemical treatments. It is found that the NC arrangement is not influenced by potential hold conditions (at 0.40 V vs. RHE) or by potential cycling in a limited potential window (V_max = 0.55 V vs. RHE). Upon potential cycling to 1.05 V vs. RHE, however, the NCs migrate on the carbon support. Interestingly, migration in oxygen or argon saturated electrolyte leads to NC coalescence, a mechanism discussed for being responsible for performance degradation of low temperature fuel cells, whereas in carbon monoxide saturated electrolyte the Pt NC agglomerate, but remain separated from each other and thus form distinctive structures.     

A new perspective on measuring the corrosion rate of localized corrosion

Many corrosion phenomena are nonuniform, which means that anodic and cathodic locations are spatially separated. An example is macrocell corrosion of steel in concrete. Under these conditions, determining the corrosion rate from polarization resistance measurements and using the Stern–Geary equation is fundamentally not possible. We present a novel theoretical approach for the interpretation of galvanostatic pulse measurements, to make them applicable as a method for corrosion rate measurements in situations of localized corrosion. Experiments show that it is important to consider that (a) only a fraction of the applied current flows through the anode of the macrocell, and (b) this current is not constant over time. We propose an approach to quantify and consider these two effects, based on information generally accessible in condition assessment of concrete structures. Our results show that galvanostatic pulse measurements are a robust method to determine the corrosion current. With the traditional empirical approach, the measurement error was generally below factor 3, and occasionally up to factor 10. With the novel approach, this error could be reduced to a factor of maximum 2 in all cases.     

Chloride induced reinforcement corrosion: Rate limiting step of early pitting corrosion

Transition from passive state to stable localised corrosion of reinforcement steel in concrete owing to chloride ingress takes place over a period of time rather than being a one-step-occurrence. The depassivation process was characterised by frequent measurements of corrosion potential, polarisation resistance, and macro-cell currents when short-circuiting the working electrode with additional cathode surface. In addition, the concrete resistivity was continuously monitored and cathodic and anodic polarisation curves were measured. The results are consistent and imply that the localised corrosion process is in the initial phase of pit growth under mixed anodic/ohmic control. With time, the anodic reaction kinetics become more limited and the corrosion rate gets almost entirely determined by anodic control. The observed relationship between achieved maximum corrosion current and concrete resistivity indicates that the extent to which the anodic reaction kinetics are restricted is determined by the concrete microstructure and its ability to retain ionic movement.     

Linking information reconciliation and privacy amplification

Information reconciliation allows two parties knowing correlated random variables, such as a noisy version of the partner's random bit string, to agree on a shared string. Privacy amplification allows two parties sharing a partially secret string about which an opponent has some partial information, to distill a shorter but almost completely secret key by communicating only over an insecure channel, as long as an upper bound on the opponent’s knowledge about the string is known. The relation between these two techniques has not been well understood. In particular, it is important to understand the effect of side-information, obtained by the opponent through an initial reconciliation step, on the size of the secret key that can be distilled safely by subsequent privacy amplification. The purpose of this paper is to provide the missing link between these techniques by presenting bounds on the reduction of the Rényi entropy of a random variable induced by side-information. We show that, except with negligible probability, each bit of side-information reduces the size of the key that can be safely distilled by at most two bits. Moreover, in the important special case of side-information and raw key data generated by many independent repetitions of a random experiment, each bit of side-information reduces the size of the secret key by only about one bit. The results have applications in unconditionally secure key agreement protocols and in quantum cryptography. This research was supported by the Swiss National Science Foundation. A preliminary version of this paper was presented at Eurocrypt '94, May 9–12, Perugia, Italy.     

Optimal Randomizer Efficiency in the Bounded-Storage Model

In the bounded-storage model for information-theoretically secure encryption and key-agreement one can prove the security of a cipher based on the sole assumption that the adversarys storage capacity is bounded, say by $s$ bits, even if her computational power is unlimited. Assume that a random $t$-bit string $R$ is either publicly available (e.g., the signal of a deep-space radio source) or broadcast by one of the legitimate parties. If $s < t$, the adversary can store only partial information about $R$. The legitimate sender Alice and receiver Bob, sharing a short secret key $K$ initially, can therefore potentially generate a very long $n$-bit one-time pad $X$ with $n\gg|K|$ about which the adversary has essentially no information. All \looseness = –1 previous results in the bounded-storage model were partial or far from optimal, for one of the following reasons: either the secret key $K$ had to be longer than the derived one-time pad ($n < |K|$), or $t$ had to be extremely large ($t > ns$), or the adversary was assumed to be able to store only $s$ actual bits of $R$ rather than arbitrary $s$ bits of information about $R$, or the adversary received a non-negligible amount of information about $X$. In this paper we prove the first non-restricted security result in the bounded-storage model: $K$ is short, $X$ is very long, and $t$ needs to be only moderately larger than $s + n$. In fact, $s/t$ can be arbitrarily close to $1$ and hence the storage bound is essentially optimal. The security can be proved also if $R$ is not uniformly random, provided that the min-entropy of $R$ is sufficiently greater than $s$.     

Chloride induced reinforcement corrosion: Electrochemical monitoring of initiation stage and chloride threshold values

Reinforcement steel embedded in six different concrete mixes was exposed to chloride by wetting/drying cycles. Various parameters were continuously monitored during more than 1 year. Cement replacement with fly ash had beneficial long-term effects regarding chloride penetration resistance. Concerning corrosion performance, by far the most dominant influencing parameter was the steel/concrete interface since corrosion initiated on the lower side of the rebar (with respect to casting direction) regardless of binder type and w/b ratio. In many cases, after the first signs of depassivation, a marked increase in chloride content was required to prevent repassivation and to enable stable pit growth.     

Short communication: Dairy consumption among middle-aged and elderly adults in Switzerland

Different studies have shown that people are aware of the benefits of dairy products, but a sizeable part of the world's population still does not consume the recommended amount of dairy produce. The aims of the present research were to determine which dairy products are consumed by the middle-aged and elderly (50–81 yr old) living in Switzerland and to explore why some of this population segment are actually reducing their consumption of dairy products. On average, older Swiss adults consumed 2.6 portions of dairy products per day, which is slightly less than the recommended 3 to 4 portions a day. Additionally, about one-quarter of the respondents indicated that they have reduced their milk or dairy consumption. The main reasons given for this decision were to reduce fat or cholesterol. A reported difficulty in digesting some dairy products may be a further reason for limiting dairy intake, particularly cheese. It follows that a need for the propagation of appropriate nutritional information about dairy products to the middle-aged and elderly exists.