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Deals with a study which proposed several kinds of direct overwrite schemes for magneto-optic media. Schemes using weakly coupled multilayers; Use of gadolinium-iron-cobalt layer having in-plane anisotropy; Impact of the use of palladium as an interlayer to control the degree of exchange interaction between memory and reference layers.

Studies the static and dynamic performance of terbium compound. Applications of magneto-optical medium; Details on the experiment; Discussion on the result of the study.

Presents a study which examined the correlation of composition and angular uniformity with performance in magneto-optic disks prepared from alloys targets. Correlation between magnetic properties and noise level; Observations on the systematic variations in the noise level and the carrier-to-noise ratio; Effect of the compositional nonuniformity on the dynamic performance of the disk.

Presents information on a study which determined the magnitude and direction of magnetization of thin metallic films using Hall effect. Proposed methods for using the Hall effect in determining the axis of a magnetic thin film; Experimental method; Results and discussion.

We present the first formal mathematical presentation of the generalized Russian cards problem, and provide rigorous security definitions that capture both basic and extended versions of weak and perfect security notions. In the generalized Russian cards problem, three players, Alice, Bob, and Cathy, are dealt a deck of $$n$$ cards, each given $$a$$, $$b$$, and $$c$$ cards, respectively. The goal is for Alice and Bob to learn each other's hands via public communication, without Cathy learning the fate of any particular card. The basic idea is that Alice announces a set of possible hands she might hold, and Bob, using knowledge of his own hand, should be able to learn Alice's cards from this announcement, but Cathy should not. Using a combinatorial approach, we are able to give a nice characterization of informative strategies (i.e., strategies allowing Bob to learn Alice's hand), having optimal communication complexity, namely the set of possible hands Alice announces must be equivalent to a large set of $$t-(n, a, 1)$$-designs, where $$t=a-c$$. We also provide some interesting necessary conditions for certain types of deals to be simultaneously informative and secure. That is, for deals satisfying $$c = a-d$$ for some $$d \ge 2$$, where $$b \ge d-1$$ and the strategy is assumed to satisfy a strong version of security (namely perfect $$(d-1)$$-security), we show that $$a = d+1$$ and hence $$c=1$$. We also give a precise characterization of informative and perfectly $$(d-1)$$-secure deals of the form $$(d+1, b, 1)$$ satisfying $$b \ge d-1$$ involving $$d-(n, d+1, 1)$$-designs. [ABSTRACT FROM AUTHOR]

Background: Chronic bronchitis (CB) in patients with COPD is associated with an accelerated lung function decline and an increased risk of respiratory infections. Despite its clinical significance, the chronic bronchitic phenotype in COPD remains poorly defined.Methods: We analyzed data from subjects enrolled in the Genetic Epidemiology of COPD (COPDGene) Study. A total of 1,061 subjects with GOLD (Global Initiative for Chronic Obstructive Lung Disease) stage II to IV were divided into two groups: CB (CB+) if subjects noted chronic cough and phlegm production for ≥ 3 mo/y for 2 consecutive years, and no CB (CB-) if they did not.Results: There were 290 and 771 subjects in the CB+ and CB- groups, respectively. Despite similar lung function, the CB+ group was younger (62.8 ± 8.4 vs 64.6 ± 8.4 years, P = .002), smoked more (57 ± 30 vs 52 ± 25 pack-years, P = .006), and had more current smokers (48% vs 27%, P < .0001). A greater percentage of the CB+ group reported nasal and ocular symptoms, wheezing, and nocturnal awakenings secondary to cough and dyspnea. History of exacerbations was higher in the CB+ group (1.21 ± 1.62 vs 0.63 ± 1.12 per patient, P < .027), and more patients in the CB+ group reported a history of severe exacerbations (26.6% vs 20.0%, P = .024). There was no difference in percent emphysema or percent gas trapping, but the CB+ group had a higher mean percent segmental airway wall area (63.2% ± 2.9% vs 62.6% ± 3.1%, P = .013).Conclusions: CB in patients with COPD is associated with worse respiratory symptoms and higher risk of exacerbations. This group may need more directed therapy targeting chronic mucus production and smoking cessation not only to improve symptoms but also to reduce risk, improve quality of life, and improve outcomes.Trial Registry: ClinicalTrials.gov; No.: NCT00608764; URL: www.clinicaltrials.gov. [ABSTRACT FROM AUTHOR]

In this paper, first we discuss the security model for deterministic challenge-response identification protocols. For such protocols, we are able to simplify the CR2 security model in [Bellare, Fischlin, Goldwasser, and Micali, Identification protocols secure against reset attacks: 495-511, Springer, 2001] which captures concurrent attacks and reset attacks. Then we propose an extremely simple identification protocol and prove that its CR2 security is equivalent to the hardness of the Strong Diffie-Hellman problem. [ABSTRACT FROM AUTHOR]

The problem of non-interactive message authentication using an insecure broadband channel and an authenticated narrow-band channel is considered. This problem has been considered in the context of ad hoc networks, where it is assumed that there is neither a secret key shared among the two parties nor a public-key infrastructure in place. A formal framework for protocols of this type is presented, along with a new protocol which is as efficient as the best previous protocols. The security of the proposed protocol is based on a new property of hash functions called ‘hybrid-collision resistance’. [ABSTRACT FROM AUTHOR]

A symmetric key cryptosystem based on logarithmic signatures for finite permutation groups was described by the first author in [6], and its algebraic properties were studied in [7]. In this paper we describe two possible approaches to the construction of new public key cryptosystems with message space a large finite group G, using logarithmic signatures and their generalizations. The first approach relies on the fact that permutations of the message space G induced by transversal logarithmic signatures almost always generate the full symmetric group S[subG] on the message space. The second approach could potentially lead to new E1Gamal-like systems based on trapdoor, one-way functions induced by logarithmic signature-like objects we call meshes, which are uniform covers for G. [ABSTRACT FROM AUTHOR]

Commitment schemes have been extensively studied since they were introduced by Blum in 1982. Rivest recently showed how to construct unconditionally secure non-interactive commitment schemes, assuming the existence of a trusted initializer. In this paper, we present a formal mathematical model for unconditionally secure non-interactive commitment schemes with a trusted initializer and analyze their binding and concealing properties. In particular, we show that such schemes cannot be perfectly binding: there is necessarily a small probability that Alice can cheat Bob by committing to one value but later revealing a different value. We prove several bounds on Alice's cheating probability, and present constructions of schemes that achieve optimal cheating probabilities. We also analyze a class of commitment schemes based on resolvable designs. [ABSTRACT FROM AUTHOR]

Inthis short note, we study all-or-nothing transforms, which wererecently proposed by Rivest as a mode of operation for blockciphers. We study transforms of this type that provide unconditionalsecurity. A simple construction for linear transforms is given,and some existence and non-existence results for general transformsare derived from a combinatorial characterization of these objects. [ABSTRACT FROM AUTHOR]

We study equidistant codes of length 4 k + 1 having (constant) weight 2 k, and (constant) distance 2 k between codewords. The maximum number of codewords is 4 k; this can be attained if and only if k = ( u + u)/2 (for some integer u) and there exists a ((2 u + 2 u + 1, u , ( u − u)/2) - SBIBD. Also, one can construct such a code, with 4 k − 1 codewords, from a (4 k − 1, 2 k − 1, k − 1) - SBIBD. [ABSTRACT FROM AUTHOR]

A Howell design of side s and order 2n, or more briefly, an H( s, 2 n), is an s× s array in which each cell either is empty or contains an unordered pair of elements from some 2 n-set, say X, such that (a) each row and each column is Latin (that is, every element of X is in precisely one cell of each row and each column) and (b) every unordered pair of elements from X is in at most one cell of the array. A trivial Howell design is an H( s, 0) having X=Ø and consisting of an s× s array of empty cells. A necessary condition on n and s for the existence of a nontrivial H( s, 2 n) is that 0< n≦ s≦2 n-1. An H( n+ t, 2 n) is said to contain a maximum trivial subdesign if some t× t subarray is the H( t, 0). This paper describes a recursive construction for Howell designs containing maximum trivial subdesigns and applies it to settle the existence question for H( n+1, 2 n)'s: for n+1 a positive integer, there is an H( n+1, 2 n) if and only if n+1 ∉ {2, 3, 5}. [ABSTRACT FROM AUTHOR]

Hanani triple systems on v≡1 (mod 6) elements are Steiner triple systems having ( v−1)/2 pairwise disjoint almost parallel classes (sets of pairwise disjoint triples that span v−1 elements), and the remaining triples form a partial parallel class. Hanani triple systems are one natural analogue of the Kirkman triple systems on v≡3 (mod 6) elements, which form the solution of the celebrated Kirkman schoolgirl problem. We prove that a Hanani triple system exists for all v≡1 (mod 6) except for v ∈ {7, 13}. [ABSTRACT FROM AUTHOR]

The main construction for resilient functions uses linear errorcorrecting codes; a resilient function constructed in this way is said to be linear. It has been conjectured that if a resilient function exists, then a linear function with the same parameters exists. In this note we construct infinite classes of nonlinear resilient functions from the Kerdock and Preparata codes. We also show that linear resilient functions having the same parameters as the functions that we construct from the Kerdock codes do not exist. Thus, the aforementioned conjecture is disproved.k [ABSTRACT FROM AUTHOR]

In this paper we continue a study of secret sharing schemes for-access structures based on graphs. Given a graph G, we require that a subset of participants can compute a secret key if they contain an edge of G; otherwise, they can obtain no information regarding the key. We study the information rate of such schemes, which measures how much information in being distributed as shares compared with the size of the secret key, and the average information rate, which is the ratio between the secret size and the arithmetic mean of the size of the shares. We give both upper and lower bounds on the optimal information rate and average information rate that can be obtained. Upper bounds arise by applying entropy arguments due to Capocelli et al. [15]. Lower bounds come from constructions that are based on graph decompositions. Application of these constructions requires solving a particular linear programming problem. We prove some general results concerning the information rate and average information rate for paths, cycles, and trees. Also, we study the 30 (connected) graphs on at most five vertices, obtaining exact values for the optimal information rate in 26 of the 30 cases, and for the optimal average information rate in 28 of the 30 cases. [ABSTRACT FROM AUTHOR]

If we agree to use one of v possible messages to communicate one of k possible source states, then an opponent can successfully impersonate a transmitter with probability at least k/v, and can successfully substitute a message with a fraudulent one with probability at least ( k−1)/( v−1). We wish to limit an opponent to these bounds. In addition, we desire that the observation of any two messages in the communication channel will give an opponent no clue as to the two source states. We describe a construction for a code which achieves these goals, and which does so with the minimum possible number of encoding rules (namely, v·( v−1)/2). The construction uses a structure from combinatorial design theory known as a perpendicular array. [ABSTRACT FROM AUTHOR]

In this paper we study secret sharing schemes for access structures based on graphs. A secret sharing scheme enables a secret key to be shared among a set of participants by distributing partial information called shares. Suppose we desire that some specified pairs of participants be able to compute the key. This gives rise in a natural way to a graph G which contains these specified pairs as its edges. The secret sharing scheme is called perfect if a pair of participants corresponding to a nonedge of G can obtain no information regarding the key. Such a perfect secret sharing scheme can be constructed for any graph. In this paper we study the information rate of these schemes, which measures how much information is being distributed as shares compared with the size of the secret key. We give several constructions for secret sharing schemes that have a higher information rate than previously known schemes. We prove the general result that, for any graph G having maximum degree d, there is a perfect secret sharing scheme realizing G in which the information rate is at least 2/( d+3). This improves the best previous general bound by a factor of almost two. [ABSTRACT FROM AUTHOR]

This paper is a study of the combinatorics of unconditionally secure secrecy and authentication codes, under the assumption that each encoding rule is to be used for the transmission of some number L of successive messages. We obtain bounds on the number of encoding rules required in order to obtain maximum levels of security. Some constructions are also given for codes which have the minimum number of encoding rules. These constructions use various types of combinatorial designs. [ABSTRACT FROM AUTHOR]

We investigate authentication codes, using the model described by Simmons. We review and generalize bounds on the probability that an opponent can deceive the transmitter/receiver by means of impersonation or substitution. Also, we give several constructions for authentication codes that meet one or more of these bounds with equality. These constructions use combinatorial designs, such as transversal designs, group-divisible designs, and BIBDs (balanced incomplete block designs). [ABSTRACT FROM AUTHOR]

Visual cryptography is a secret sharing scheme that uses the human visual system to perform computations. In this article, we present some background to traditional secret-sharing schemes, then explain visual schemes, describing some of the basic construction techniques used. topics discussed include: two out of two scheme, two out of n schemes, and graph access structures [ABSTRACT FROM PUBLISHER]

In this paper we construct pairwise balanced designs (PBDs) having block sizes which are prime powers congruent to 1 modulo 6. Such a PBD contains n = 6r + 1 points, for some positive integer r. We show that this condition is sufficient for n ≥ 1927, with at most 31 possible exceptions below this value. As an immediate corollary, we prove that there exists a pair of orthogonal Steiner triple systems of order n, for the same values of n. [ABSTRACT FROM AUTHOR]

In this paper we provide upper and lower bounds on the randomness required by the dealer to set up a secret sharing scheme for infinite classes of access structures. Lower bounds are obtained using entropy arguments. Upper bounds derive from a decomposition construction based on combinatorial designs (in particular, t-(v,k,λ) designs). We prove a general result on the randomness needed to construct a scheme for the cycle Cn; when n is odd our bound is tight. We study the access structures on at most four participants and the connected graphs on five vertices, obtaining exact values for the randomness for all them. Also, we analyze the number of random bits required to construct anonymous threshold schemes, giving upper bounds. (Informally, anonymous threshold schemes are schemes in which the secret can be reconstructed without knowledge of which participants hold which shares.) [ABSTRACT FROM AUTHOR]

We consider a pair of MOLS (mutually orthogonal Latin squares) having holes, corresponding to missing sub-MOLS, which are disjoint and spanning It is shown that a pair of MOLS with n holes of size h exist for h ≥ 2 if and only if n ≥ 4 For SOLS (self-orthogonal Latin squares) with holes, we have the same result, with two possible exceptions SOLS with 7 or 13 holes of size 6 [ABSTRACT FROM AUTHOR]

A spread in PG( n, q) is a set of lines which partitions the point set. A packing in PG( n, q) ( n odd) is a partition of the lines into spreads. Two packings of PG( n, q) are called orthogonal if and only if any two spreads, one from each packing, have at most one line in common. Recently, R. D. Baker has shown the existence of a pair of orthogonal packings in PG(5, 2). In this paper we enumerate all packings in PG(5, 2) having both an automorphism of order 31 and the Frobenius automorphism. We find all pairs of orthogonal packings of the above type and display a set of six mutually orthogonal packings. Previously the largest set of orthogonal packings known in PG(5, 2) was two. [ABSTRACT FROM AUTHOR]

A Room square of even side cannot exist. We study arrays of even side which very closely resemble Room squares. The spectrum is determined: the desired arrays exist for all even sides exceeding 4. These arrays are useful in a construction for Room squares containing subsquares. It is shown that, for all n≧4, and all odd r≧7 (except r=11), there is a Room square of side nr + n − 1 which contains subsquares of sides r and 2 n − 1. [ABSTRACT FROM AUTHOR]

It is shown that there exists a resolvable n by 4 orthogonal array which is invariant under the Klein 4-group K for all positive integers n congruent to 0 modulo 4 except possibly for n ∈ {12, 24, 156, 348}. [ABSTRACT FROM AUTHOR]

A Steiner triple system can be nested if it is possible to add one point to each block in such a way that a BIBD with block-size 4 and λ=1 is obtained. We prove that there exists a Steiner triple system of order v that can be nested if and only if vэ1 mod 6. [ABSTRACT FROM AUTHOR]