In this work private information retrieval (PIR) codes are studied. In a k-PIR code, s information bits are encoded in such a way that every information bit has k mutually disjoint recovery sets. The main problem under this paradigm is to minimize the number of encoded bits given the values of s and k, where this value is denoted by P(s, k). The main focus of this work is to analyze P(s, k) for a large

An extending theorem for s-resolvable t-designs is presented, which may be viewed as an extension of Qiu-rong Wu’s result. The theorem yields recursive constructions for s-resolvable t-designs, and mutually disjoint t-designs. For example, it can be shown that if there exists a large set LS[29](4, 5, 33), then there exists a family of 3-resolvable 4-\((5+29m, 6, \frac{5}{2}m(1+29m) )\) designs for

A \((v,k,\lambda )\) symmetric design is said to have the symmetric difference property (SDP) if the symmetric difference of any three blocks is either a block or the complement of a block. The designs associated to the symplectic difference sets introduced by Kantor (J Algebra 33:43–58, 1975) have the SDP. Parker (J Comb Theory Ser A 67:23–43, 1994) claimed that the symplectic design on 64 points

A frequency square is a square matrix in which each row and column is a permutation of the same multiset of symbols. A frequency square is of type \((n;\lambda )\) if it contains \(n/\lambda \) symbols, each of which occurs \(\lambda \) times per row and \(\lambda \) times per column. In the case when \(\lambda =n/2\) we refer to the frequency square as binary. A set of k-MOFS\((n;\lambda )\) is a

We consider approximability of two optimization problems called Minimum Open k-Monopoly (Min-Open-k-Monopoly) and Minimum Partial Open k-Monopoly (Min-P-Open-k-Monopoly), where k is a fixed positive integer. The objective, in Min-Open-k-Monopoly, is to find a minimum cardinality vertex set \(S \subseteq V\) in a given graph G = (V,E) such that \(|N(v) \cap S| \geq \frac {1}{2} |N(v)| + k\), for every

Abstract Given elements a, b, c of any associative ring R with 1, then a is called right hybrid (b, c)-invertible if there exists y ∈ R such that yay = y , y R = b R and rann ( y ) = rann ( c ) . It is shown that such y exists if and only if c ∈ cabR and rann ( cab ) ⊆ rann ( b ) , in which case y is unique. With an appropriate generalization of the right annhilator rann (.), this result is extended

Abstract For an element w of a simply-laced Weyl group, Buan-Iyama-Reiten-Scott defined a subcategory F ( w ) of the module category over the preprojective algebra of Dynkin type. This paper studies categorical properties of F ( w ) using the root system. We show that simple objects in F ( w ) bijectively correspond to Bruhat inversion roots of w, and obtain a combinatorial criterion for F ( w ) to

Abstract The aim of this article is to provide an answer to the C [ ∂ ] -split extending structures problem for Leibniz conformal algebras, which asks that how to describe all Leibniz conformal algebra structures on E = R ⊕ Q up to an isomorphism such that R is a Leibniz conformal subalgebra. For this purpose, a unified product of Leibniz conformal algebras is introduced. Using this tool, two cohomological

Abstract In this paper, we investigate Lie generalized derivations on bound quiver algebras associated with a finite acyclic quiver. The first main result shows that every bound quiver algebra associated with a finite acyclic quiver has the properness Lie generalized derivation property. The second main result investigates the uniqueness property. Namely, among other things, we show that a bound quiver

Let \(m=8k\) and \(\alpha\) be a primitive element of the finite field \({{\mathbb {G}}{\mathbb {F}}}(2^m)\), where \(k\ge 2\) is an integer. In this paper, a class of binary cyclic codes \({{\mathcal {C}}}_{(u,v)}\) of length \(2^m-1\) with two nonzeros \(\alpha ^{-u}\) and \(\alpha ^{-v}\) is studied, where \((u,v)=(1,(2^{m}-1)/17)\). It turns out that \({{\mathcal {C}}}_{(u,v)}\) has parameters

A finitely generated group acting on a tree so that all vertex and edge stabilizers are infinite cyclic groups is called a generalized Baumslag–Solitar group (a GBS group). Every GBS group is the fundamental group π1(𝔸) of a suitable labeled graph 𝔸. We prove that if 𝔸 and 𝔹 are labeled trees, then the groups π1(𝔸) and π1(𝔹) are universally equivalent iff π1(𝔸) and π1(𝔹) are embeddable into

We study the deformations of a curve C on an Enriques-Fano 3-fold X⊂Pn, assuming that C is contained in a smooth hyperplane section S⊂X, that is a smooth Enriques surface in X. We give a sufficient condition for C to be (un)obstructed in X, in terms of half pencils and (−2)-curves on S. Let HilbscX denote the Hilbert scheme of smooth connected curves in X. By using the Hilbert-flag scheme of X, we

Joyce showed that for a classical knot K, the involutory medial quandle IMQ(K) is isomorphic to the core quandle of the homology group H1(X2), where X2 is the cyclic double cover of 𝕊3, branched over K. It follows that |IMQ(K)|=|detK|. In this paper, the extension of Joyce’s result to classical links is discussed. Among other things, we show that for a classical link L of μ≥2 components, the order

First Grigorchuk group 𝒢 and Grigorchuk’s overgroup 𝒢̃, introduced in 1980, are self-similar branch groups with intermediate growth. In 1984, 𝒢 was used to construct the family of generalized Grigorchuk groups {Gω|ω∈{0,1,2}ℕ}, which has many remarkable properties. Following this construction, we generalize the Grigorchuk’s overgroup 𝒢̃ to the family {G̃ω|ω∈{0,1,2}ℕ} of generalized Grigorchuk’s

For q=3r (r∈ℕ), denote by 𝔽q the finite field of order q and for a positive integer m≥2, let 𝔽qm be its extension field of degree m. We establish a sufficient condition for existence of a primitive normal element α such that f(α) is a primitive element, where f(x)=ax2+bx+c, with a,b,c∈𝔽qm satisfying b2≠ac in 𝔽qm.

This paper considers a new alphabet set, which is a ring that we call 𝔽4R, to construct linear error-control codes. Skew cyclic codes over this ring are then investigated in details. We define a nondegenerate inner product and provide a criteria to test for self-orthogonality. Results on the algebraic structures lead us to characterize 𝔽4R-skew cyclic codes. Interesting connections between the image

We introduce two groups of duplication processes that extend the well known Cayley–Dickson process. The first one allows to embed every 4-dimensional (4D) real unital algebra 𝒜 into an 8D real unital algebra denoted by FD(𝒜). We also find the conditions on 𝒜 under which FD(𝒜) is a division algebra. This covers the most classes of known 4D real division algebras. The second process allows us to

We investigate the structure and properties of an Artinian monomial complete intersection quotient A(n,d)=𝕂[x1,…,xn]/(x1d,…,xnd). We construct explicit homogeneous bases of A(n,d) that are compatible with the Sn-module structure for n=3, all exponents d≥3 and all homogeneous degrees j≥0. Moreover, we derive the multiplicity formulas, both in recursive form and in closed form, for each irreducible

Let (A,𝔪) be a Noetherian local ring of dimension d>0 and I an 𝔪-primary ideal of A. In this paper, we discuss a sufficient condition, for the Buchsbaumness of the local ring A to be passed onto the associated graded ring of filtration. Let ℐ denote an I-good filtration. We prove that if A is Buchsbaum and the 𝕀 -invariant, 𝕀(A) and 𝕀(G(ℐ)), coincide then the associated graded ring G(ℐ) is Buchsbaum

Let Γ(R), ΓE(R), ΓAnn(R) denote the zero-divisor graph, compressed zero-divisor graph and annihilating ideal graph of a commutative ring R, respectively. In this paper, we prove that ΓE(R)≅ΓAnn(R) for a semisimple commutative ring R and represent Γ(R) as a generalized join of a finite set of graphs. Further, we study the zero-divisor graph of a semisimple group-ring 𝔽qCn and proved several structural

We prove an analogue of the Kac–Wakimoto conjecture for the periplectic Lie superalgebra 𝔭(n), stating that any simple module lying in a block of non-maximal atypicality has superdimension zero.

In this paper, we consider semisimple group algebras 𝔽qG of split metacyclic groups over finite fields. We construct left codes in 𝔽qG in the case when the order G is pmℓn, where p and ℓ are different primes such that gcd(q,p,ℓ)=1 extend the construction described in a previous paper, determine their dual codes and find some good codes.

Let Cn denote the cyclic group of order n, and let Hol(Cn) denote the holomorph of Cn. In this paper, for any odd integer m≥3, we find necessary and sufficient conditions on an integer A, with |A|≥3, such that 𝔉m,A(x)=x2m+Axm+1 is irreducible over ℚ. When m=q≥3 is prime and 𝔉q,A(x) is irreducible, we show that the Galois group over ℚ of 𝔉q,A(x) is isomorphic to either Hol(Cq) or Hol(C2q), depending

Let R be a commutative ring, we say that 𝒜⊆Spec(R) has prime avoidance property, if I⊆⋃P∈𝒜P for an ideal I of R, then there exists P∈𝒜 such that I⊆P. We exactly determine when 𝒜⊆Spec(R) has prime avoidance property. In particular, if 𝒜 has prime avoidance property, then 𝒜 is compact. For certain classical rings we show the converse holds (such as Bezout rings, QR-domains, zero-dimensional rings

Let (R,𝔪) be a commutative Noetherian complete local ring and I be a proper ideal of R. Suppose that M is a nonzero I-cofinite R-module of Krull dimension n. In this paper, it shown that dimR/(I+AnnRH𝔪n(M))=n. As an application of this result, it is shown that dimR/(I+𝔭)=n, for each 𝔭∈AttRH𝔪n(M). Also it shown that for each j≥0 the submodule Σj(M):=∪{K:K≤M and dimK≤j} of M is I-cofinite, dimR

Simplicial complexes (here briefly complexes) are set systems on an arbitrary set which are object of study in many areas of both mathematics and theoretical computer science. Usually, they are investigated over finite sets. However, in general, when we consider an arbitrary set Ω (not necessarily finite) and a complex 𝒞 on Ω, the most natural property related to finiteness is the following: for any

We study the representation theory of finite-dimensional ω-Lie algebras over the complex field. We derive an ω-Lie version of the classical Lie’s theorem, i.e., any finite-dimensional irreducible module of a soluble ω-Lie algebra is 1-dimensional (1D). We also prove that indecomposable modules of some 3D ω-Lie algebras could be parametrized by the complex field and nilpotent matrices. We introduce

We continue the algebraic study of almost inner derivations of Lie algebras over a field of characteristic zero and determine these derivations for free nilpotent Lie algebras, for almost abelian Lie algebras, for Lie algebras whose solvable radical is abelian and for several classes of filiform nilpotent Lie algebras. We find a family of n-dimensional characteristically nilpotent filiform Lie algebras

By an additive action on an algebraic variety X we mean a regular effective action 𝔾an×X→X with an open orbit of the commutative unipotent group 𝔾an. In this paper, we give a classification of additive actions on complete toric surfaces.

For two bimodules NBA and MAB with M⊗AN=0=N⊗BM, the monomorphism category M(A,M,N,B) and its dual, the epimorphism E(A,M,N,B), are introduced and studied. By definition, M(A,M,N,B) is the subcategory of Δ-mod consisting of (X,Y,f,g) such that f:M⊗AX→Y is a monic B-map and g:N⊗BY→X is a monic A-map, where Δ=(ANMB) is a Morita ring. This monomorphism category is a resolving subcategory of Δ-mod if and

We describe a general technique to classify blocks of finite groups, and we apply it to determine Morita equivalence classes of blocks with elementary abelian defect groups of order 32 with respect to a complete discrete valuation ring with an algebraically closed residue field of characteristic two. As a consequence we verify that a conjecture of Harada holds on these blocks.

Let F be the maximal totally real subfield of ℚ(ζ32), the cyclotomic field of 32-nd roots of unity. Let D be the quaternion algebra over F ramified exactly at the unique prime above 2 and 7 of the real places of F. Let 𝒪 be a maximal order in D, and X0D(1) the Shimura curve attached to 𝒪. Let C = X0D(1)∕⟨wD⟩, where wD is the unique Atkin–Lehner involution on X0D(1). We show that the curve C has several

Let k be a perfect field of characteristic p > 2, and let K be a finite totally ramified extension over W(k)[1 p] of ramification degree e. Let R0 be a relative base ring over W(k)⟨t1±1,…,tm±1⟩ satisfying some mild conditions, and let R = R0 ⊗W(k)𝒪K. We show that if e < p − 1, then every crystalline representation of π1e ́ t(SpecR[1 p]) with Hodge–Tate weights in [0,1] arises from a p-divisible group

Abstract In this paper, we introduce and study a generalization of powerful ideals, in the sense of Badawi and Houston, to the context of integral domains graded by a torsionless monoid.

We study algebras generated by idempotents. For finite dimensional algebras over a field, it turns out that these algebras can be characterized by their irreducible modules homologically. Particularly, we obtain that a finite dimensional algebra over an algebraically closed field is generated by idempotents if and only if ExtA1(S,S)=0 for all 1-dimensional A-modules S.

Let A be the fiber product R×TB, where B→T is a surjective ring homomorphism with regular kernel and R⊆T is a ring extension where T is an overring of R. In this paper we provide a characterization of when A has distinguished Prüfer-like properties and new constructions of Prüfer rings with zero-divisors. Furthermore we give examples of homomorphic images of Prüfer rings that are Prüfer without assuming

The well-known Thompson theorem on character degrees states that if a prime p divides the degree of every nonlinear irreducible character of a finite group G, then G is p-nilpotent. In this paper, we give a strengthened version of Thompson's theorem in terms of ∑χ∈Irrp′(G)χ(1) and ∑χ∈Irrp′(G)χ(1)2, where Irrp′(G) denotes the set of all ordinary irreducible characters of G of degree coprime to p.

An important problem in the representation theory of affine and toroidal Lie algebras is to classify all possible irreducible integrable modules with finite-dimensional weight spaces. Recently the irreducible integrable modules having finite-dimensional weight spaces with non-trivial central action have been classified for a more general class of Lie algebras, namely the graded Lie tori. In this paper

In this paper we study associative unitary superalgebras with graded involution or superinvolution having polynomial growth of the codimension sequence. The first goal is to prove that, for this kind of algebras, the codimension sequence is a polynomial with rational coefficients. Then we shall construct several superalgebras with graded involution or superinvolution realizing the smallest and the

We show that the minimal log discrepancy of any Q-Gorenstein non-canonical threefold is ≤1213, which is an optimal bound.

Let (K,v) be a valued field, and μ an inductive valuation on K[x] extending v. Let Gμ be the graded algebra of μ over K[x], and κ the maximal subfield of the subring of Gμ formed by the homogeneous elements of degree zero. In this paper, we find an algorithm to compute the field κ and the residual polynomial operator Rμ:K[x]→κ[y], where y is another indeterminate, without any need to perform computations

In prime characteristic there are important invariants that allow us to measure singularities. For certain cases, it is known that they are rational numbers. In this article, we show this property for Stanley-Reisner rings in several cases.

We introduce the extension groups between atoms in an abelian category. For a locally noetherian Grothendieck category, the localizing subcategories closed under injective envelopes are characterized in terms of those extension groups. We also introduce the virtual duals of the extension groups between atoms to measure the global dimension of the category. A new topological property of atom spectra

The degree of a projective subscheme has an upper bound deg(X)≤(e+re) in terms of the codimension e and the reduction number r. It was proved in [3] that deg(X)=(e+re) if and only if X is arithmetically Cohen-Macaulay and has an (r+1)-linear resolution. Moreover, if the degree of a projective variety X satisfies deg(X)=(e+re)−1, then the Betti table is described with some constraints. In this paper

We answer two questions of Carrell on a singular complex projective variety admitting the multiplicative group action, one positively and the other negatively. The results are applied to Chow varieties and we obtain Chow groups of 0-cycles and Lawson homology groups of 1-cycles for Chow varieties. A brief survey on the structure of Chow varieties is included for comparison and completeness. Moreover

In this paper, we propose a robust framework based on the scaled boundary finite element method to model implicit interfaces in two-dimensional differential equations in nonhomegeneous media. The salient features of the proposed work are: (a) interfaces can be implicitly defined and need not conform to the background mesh; (b) Dirichlet boundary conditions can be imposed directly along the interface;

In this article we explore an approach to the problem of Albert described by U. Umirbaev. We characterize the space of invariant bilinear forms of the polarization algebra of a polynomial endomorphism F:Kn→Kn, where K is a field with characteristic different from two. We obtain some conjectures expressed in the language of polynomial endomorphisms, which are equivalent to the existence of invariant

In this paper, we introduce a class of exact structures in terms of finiteness conditions of modules, which are called n-pure exact structures. We investigate the properties of n-pure derived categories of module categories using n-pure exact structures, and show that n-pure derived categories share many nice properties of classical derived categories. In particular, we show that bounded n-pure derived

In [6] and [7], Joyce and Matveev showed that for given a group G and an automorphism ϕ, there is a quandle structure on the underlying set of G. When the automorphism is an inner-automorphism by ζ, we denote this quandle structure as (G,◃ζ). In this paper, we show a relationship between group extensions of a group G and quandle extensions of the quandle (G,◃ζ). In fact, there exists a group homomorphism

We prove that δ-derivations of a simple finite-dimensional Lie algebra over a field of characteristic zero, with values in a finite-dimensional module, are either inner derivations, or, in the case of adjoint module, multiplications by a scalar, or some exceptional cases related to sl(2). This can be viewed as an extension of the classical first Whitehead Lemma.

We study a simple, self-dual, rational, and C2-cofinite vertex operator algebra of CFT-type whose simple current modules are graded by Z2k. Based on those simple current modules, a vertex operator algebra associated with a Z2k-code is constructed. The classification of irreducible modules for such a vertex operator algebra is established. Furthermore, all the irreducible modules are realized in a module

In 2007, Dubouloz introduced Danielewski varieties. Such varieties generalize Danielewski surfaces and provide counterexamples to generalized Zariski cancellation problem in arbitrary dimension. In the present work we describe the automorphism group of a Danielewski variety. This result is a generalization of a description of automorphisms of Danielewski surfaces due to Makar-Limanov.

One proves a far-reaching upper bound for the degree of a generically finite rational map between projective varieties over a base field of arbitrary characteristic. The bound is expressed as a product of certain degrees that appear naturally by considering the Rees algebra (blowup) of the base ideal defining the map. Several special cases are obtained as consequences, some of which cover and extend

In this paper we study the Galois group of the Galois cover of the composition of a q-cyclic étale cover and a cyclic p-gonal cover for any odd prime p. Furthermore, we give properties of isogenous decompositions of certain Prym and Jacobian varieties associated to intermediate subcovers given by subgroups.

We provide a classification of developable cubic hypersurfaces in P4. Using the correspondence between forms of degree 3 on P4 and Artinian Gorenstein K-algebras, given by Macaulay-Matlis duality, we describe the locus in GOR(1,5,5,1) corresponding to those algebras which satisfy the Strong Lefschetz property.

We construct a uniform model for highest weight crystals and B(∞) for generalized Kac–Moody algebras using rigged configurations. We also show an explicit description of the ⁎-involution on rigged configurations for B(∞): that the ⁎-involution interchanges the rigging and the corigging. We do this by giving a recognition theorem for B(∞) using the ⁎-involution. As a consequence, we also characterize

We study the problem when the product of two non-linear Galois conjugate characters of a finite group are irreducible. We also prove new results on irreducible tensor products of cross-characteristic Brauer characters of quasisimple groups of Lie type.

Let U1,U2 be connected commutative unipotent algebraic groups defined over an algebraically closed field k of characteristic p>0 and let L be a bimultiplicative Q‾ℓ-local system on U1×U2. In this paper we will study the Q‾ℓ-cohomology Hc⁎(U1×U2,L), which turns out to be supported in only one degree. We will construct a finite Heisenberg group Γ which naturally acts on Hc⁎(U1×U2,L) as an irreducible

Let X be a weighted projective line and CX the associated cluster category. It is known that CX can be realized as a generalized cluster category of quiver with potential. In this note, under the assumption that X has at most three weights or is of tubular type, we prove that if the generalized cluster category C(Q,W) of a Jacobi-finite non-degenerate quiver with potential (Q,W) shares a 2-CY tilted

The objects of study in this paper are Hopf algebras H which are finitely generated algebras over an algebraically closed field and are extensions of a commutative Hopf algebra A by a finite dimensional Hopf algebra H‾:=H/A+H, where A+ is the augmentation ideal of A. Basic structural and homological properties are recalled and classes of examples are listed. A structure theorem is proved when (⁎) H‾