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Pu Zhang

Publications and source records attributed to Pu Zhang.

104 records · Page 6Linked to original sources
arXiv2011

Auslander-Reiten translations in monomorphism categories

We generalize Ringel and Schmidmeier's theory on the Auslander-Reiten translation of the submodule category $\mathcal S_2(A)$ to the monomorphism category $\mathcal S_n(A)$. As in the case of $n=2$, $\mathcal S_n(A)$ has Auslander-Reiten sequences, and the Auslander-Reiten translation $τ_{\mathcal{S}}$ of $\mathcal S_n(A)$ can be explicitly formulated via $τ$ of $A$-mod. Furthermore, if $A$ is a selfinjective algebra, we study the periodicity of $τ_{\mathcal{S}}$ on the objects of $\mathcal S_n(A)$, and of the Serre functor $F_{\mathcal S}$ on the objects of the stable monomorphism category $\underline{\mathcal{S}_n(A)}$. In particular, $τ_{\mathcal S}^{2m(n+1)}X\cong X$ for $X\in\mathcal{S}_n(\A(m, t))$; and $F_{\mathcal S}^{m(n+1)}X\cong X$ for $X\in\underline{\mathcal{S}_n(\A(m, t))}$, where $\A(m, t), \ m\ge1, \ t\ge2,$ are the selfinjective Nakayama algebras.

math.RT↗
arXiv2011

Symmetric recollements induced by bimodule extensions

nspired by the work of J$ø$rgensen [J], we define a (upper-, lower-) symmetric recollements; and give a one-one correspondence between the equivalent classes of the upper-symmetric recollements and one of the lower-symmetric recollements, of a triangulated category. Let $\m = \left(\begin{smallmatrix} A&M 0&B \end{smallmatrix}\right)$ with bimodule $_AM_B$. We construct an upper-symmetric abelian category recollement of $\m$-mod; and a symmetric triangulated category recollement of $\underline {\m\mbox{-}\mathcal Gproj}$ if $A$ and $B$ are Gorenstein and $_AM$ and $M_B$ are projective.

math.RT↗
arXiv2011

Monomorphism categories, cotilting theory, and Gorenstein-projective modules

The monomorphism category $\mathcal S_n(\mathcal X)$ is introduced, where $\mathcal X$ is a full subcategory of the module category $A$-mod of Artin algebra $A$. The key result is a reciprocity of the monomorphism operator $\mathcal S_n$ and the left perpendicular operator $^\perp$: for a cotilting $A$-module $T$, there is a canonical construction of a cotilting $T_n(A)$-module ${\rm \bf m}(T)$, such that $\mathcal S_n(^\perp T) = \ ^\perp {\rm \bf m}(T)$. As applications, $\mathcal S_n(\mathcal X)$ is a resolving contravariantly finite subcategory in $T_n(A)$-mod with $\hat{\mathcal S_n(\mathcal X)} = T_n(A)$-mod if and only if $\mathcal X$ is a resolving contravariantly finite subcategory in $A$-mod with $\hat{\mathcal X} = A$-mod. For a Gorenstein algebra $A$, the category $T_n(A)\mbox{-}\mathcal Gproj$ of Gorenstein-projective $T_n(A)$-modules can be explicitly determined as $\mathcal S_n(^\perp A)$. Also, self-injective algebras $A$ can be characterized by the property $T_n(A)\mbox{-}\mathcal Gproj = \mathcal S_n(A)$. Using $\mathcal S_n(A)= \ ^\perp {\rm \bf m}(D(A_A))$, a characterization of $\mathcal S_n(A)$ of finite type is obtained.

math.RT↗
arXiv2010

Abnormal enhancement of electric field inside a thin permittivity-near-zero object in free space

It is found that the electric field can be enhanced strongly inside a permittivity-near-zero object in free space, when the transverse cross section of the object is small and the length along the propagation direction of the incident wave is large enough as compared with the wavelength. The physical mechanism is explained in details. The incident electromagnetic energy can only flow almost normally through the outer surface into or out of the permittivity-near-zero object, which leads to large energy stream density and then strong electric field inside the object. Meanwhile, the magnetic field inside the permittivity-near-zero object may be smaller than that of the incident wave, which is also helpful for enhancing the electric field. Two permittivity-near-zero objects of simple shapes, namely, a thin cylindrical shell and a long thin rectangular bar, are chosen for numerical illustration. The enhancement of the electric field becomes stronger when the permittivity-near-zero object becomes thinner. The physical mechanism of the field enhancement is completely different from the plasmonic resonance enhancement at a metal surface.

physics.optics↗
arXiv2010

Carpet cloaking on a dielectric half-space

Carpet cloaking is proposed to hide an object on a dielectric half-space from electromagnetic (EM) detection. A two-dimensional conformal transformation specified by an analytic function is utilized for the design. Only one nonsingular material parameter distribution suffices for the characterization. The cloaking cover situates on the dielectric half-space, and consists of a lossless upper part for EM wave redirection and an absorbing bottom layer for inducing correct reflection coefficient and absorbing transmission. Numerical simulations with Gaussian beam incidence are performed for verification.

physics.optics↗
arXiv2010

Squeezing electromagnetic energy with a dielectric split ring inside a permeability-near-zero metamaterial

A novel electromagnetic energy squeezing mechanism is proposed based on the special properties of permeability-near-zero metamaterials. Nearly no energy stream can enter a conventional dielectric region positioned inside a permeability-near-zero material. When a source is surrounded by a dielectric split ring (encloser with a gap opened), the electromagnetic energy generated by the source is forced to propagate through the gap. When the gap is narrow, the energy stream density becomes very large and makes the magnetic field enhanced drastically in the gap. The narrow gap can be long and bended. This provides us a method to obtain strong magnetic field without using resonance enhancement.

physics.optics↗
arXiv2009

Inverse Transformation Optics and Reflection Analysis for Two-Dimensional Finite Embedded Coordinate Transformation

Inverse transformation optics is introduced, and used to calculate the reflection at the boundary of a transformation medium under consideration. The transformation medium for a practical device is obtained from a two-dimensional (2D) finite embedded coordinate transformation (FECT) which is discontinuous at the boundary. For an electromagnetic excitation of particular polarization, many pairs of original medium (in a virtual space V') and inverse transformation can give exactly the same anisotropic medium through the conventional procedure of transformation optics. Non-uniqueness of these pairs is then exploited for the analysis and calculation of the boundary reflection. The reflection at the boundary of the anisotropic FECT medium (associated with the corresponding vacuum virtual space V) is converted to the simple reflection between two isotropic media in virtual space V' by a selected inverse transformation continuous at the boundary. A reflectionless condition for the boundary of the FECT medium is found as a special case. The theory is verified numerically with the finite element method.

physics.optics↗
arXiv2007

Quotient triangulated categories

For a self-orthogonal module $T$, the relation between the quotient triangulated category $D^b(A)/K^b({\rm add} T)$ and the stable category of the Frobenius category of $T$-Cohen-Macaulay modules is investigated. In particular, for a Gorenstein algebra, we get a relative version of the description of the singularity category due to Happel. Also, the derived category of a Gorenstein algebra is explicitly given, inside the stable category of the graded module category of the corresponding trivial extension algebra, via Happel's functor $F: D^b(A) \longrightarrow T(A)^{\mathbb{Z}}{-}\underline{\rm mod}$.

math.RT↗
arXiv2006

Calabi-Yau objects in triangulated categories

We introduce the Calabi-Yau (CY) objects in a Hom-finite Krull-Schmidt triangulated $k$-category, and notice that the structure of the minimal, consequently all the CY objects, can be described. The relation between indecomposable CY objects and Auslander-Reiten triangles is provided. Finally we classify all the CY modules of self-injective Nakayama algebras, determining this way the self-injective Nakayama algebras admitting indecomposable CY modules. In particular, this result recovers the algebras whose stable categories are Calabi-Yau, which have been obtained in [BS].

math.RT↗
arXiv2005

Commutators of integral operators with variable kernels on Hardy spaces

Let $\T (0\leq α<n)$ be the singular and fractional integrals with variable kernel $Ω(x,z)$, and $[b,\T]$ be the commutator generated by $\T$ and a Lipschitz function $b$. In this paper, the authors study the boundedness of $[b,\T]$ on the Hardy spaces, under some assumptions such as the $L^r$-Dini condition. Similar results and the weak type estimates at the end-point cases are also given for the homogeneous convolution operators $\tT (0\leq α<n)$. The smoothness conditions imposed on $\tOmega$ are weaker than the corresponding known results.

math.CA↗
arXiv2004

Monomial Hopf Algebras

Let $K$ be a field of characteristic 0 containing all roots of unity. We classify all the Hopf structures on monomial $K$-coalgebras, or, in dual version, on monomial $K$-algebras.

math.QA↗
arXiv2004

Dual Gabriel Theorem with applications

We introduce the quiver of a bicomodule over a cosemisimple coalgebra. Applying this to the coradical $C_0$ of an arbitrary coalgebra $C$, we give an alternative definition of the Gabriel quiver of $C$, and then show that it coincides with the known $\operatorname {Ext}$ quiver of $C$ and the link quiver of $C$. The dual Gabriel theorem for a coalgebra with separable coradical is obtained, which generalizes the corresponding result for a pointed coalgebra. We also give a new description of $C_1$ of any coalgebra $C$, which can be regarded as a generalization of the first part of the well-known Taft-Wilson Theorem for pointed coalgebras. As applications, we give a characterization of locally finite coalgebras via their Gabriel quivers, and a property of the Gabriel quiver of a quasi-coFrobenius coalgebra.

math.RT↗
arXiv2004

Comodules of $U_q(sl_2)$ and modules of $SL_q(2)$ via quiver

The aim of this paper is to construct comodules of $U_q(sl_2)$ and modules of $SL_q(2)$ via quiver, where $q$ is not a root of unity. By embedding the quantized algebra $U_q(sl_2)$ into the path coalgebra $k\mathcal{D}^c$, where $\mathcal{D}$ is the Gabriel quiver of $U_q(sl_2)$ as a coalgebra, we obtain a basis of $U_q(sl_2)$ in terms of combinations of paths in the quiver $\mathcal{D}$; this special basis enable us to describe the category of $U_q(sl_2)$-comodules by certain representations of $\mathcal{D}$; and this description further permits us to construct a class of modules of the quantum special linear group $SL_q(2)$, from certain representations of $\mathcal{D}$, via the duality between $U_q(sl_2)$ and $SL_q(2)$.

math.QA↗