Visszutas logisztika és termeléstervezés (Reverse logistics and production planning)

A dolgozat a visszutas logisztikát, az újrahasznosítást igyekszik beilleszteni a vállalati termeléstervezés keretei közé. A szükséglettervezési rendszerek (material requirements planning, MRP) célja a készletek és beszerzendő anyagok, alkatrészek időben ütemezett gyártásának és beszerzésének megtervezése. A klasszikus MRP rendszereket az utóbbi időben próbálja a tudomány az újrahasznosítással kibővíteni. Mivel ebben az esetben az új, és újrafelhasználható anyagokat külön kell nyilvántartani, ezért az MRP-táblák és készletek növekednek. A rendelési tételnagyságok meghatározása is nehezebb, összetettebb tételnagysághoz vezet. A dolgozatban egy visszutas logisztikai készletmodellt ismertetünk, valamint annak dinamikus kiterjesztését, amely alapja lehet az SAP-ba beépíthető rendelés állomány meghatározó heurisztikának. ____ The aim of the paper is to extend production planning with reverse logistics and reuse. Material requirements planning (MRP) systems plan and control invetory levels and purchasing activities of the firm. In the last decade scientists on this field try to involve reverse logistics activities in MRP systems. Size of MRP-tables is growing in this case because of the alternative use of newly purchased products and reusable old items. Determination of order quantities will be more complex with these two modes of material supplies. An EOQ-type reverse logistics model is presented in the paper with a dynamic lot size generalization. The generalized model can be seen as a basic model to build in production planning and control system like SAP.

A vállalati logisztikai költségek a magyarországi kis- és középvállalkozások körében végzett felmérés tükrében (Corporate logistics costs of the Hungarian small- and medium-sized enterprises)

A cikk a magyarországi kis- és középvállalkozások logisztikai költségeit vizsgálja a nemzetközi kutatások tükrében és a 2009-es közel kétezer hazai KKV-re kiterjedő „Vállalkozások helyzetének felmérése” alapján. A hazai logisztikai költségeket leginkább a vállalatméret és az ágazat befolyásolja. A magyarországi kis- és középvállalkozások ki nem szervezett szállítási és raktározási tevékenységei a hazai fuvarozóknak és raktárszolgáltatóknak jelentős piacbővülést jelenthetnének. Ez azonban csak látens piacbővülés, mivel a hazai KKV-k nem tervezik, hogy szállítási és raktározási tevékenységeiket nagyobb arányban szervezzék ki. Ez részben azzal magyarázható, hogy a feldolgozóipari, mezőgazdasági és kereskedő kis- és középvállalkozások viszonylag nagy arányban tekintik a logisztikát alapvető képességnek. Nemzetközi viszonylatban a magyarországi KKV-k magas logisztikai költségszintekkel szembesülnek, melynek mérséklésével az adminisztrációs terhek csökkentéséhez hasonló megtakarítást lehetne elérni. ____ This article examines total logistics costs and its components of the Hungarian small- and medium-sized enterprises in the light of international researches. It shows that company-size and its sector are the most important drivers of logistics costs and its components according to „Survey of position of enterprises”, which covered nearly 2000 Hungarian SMEs in 2009. It also proves that transport and warehousing demand of the Hungarian SMEs means a significant market growth for national carriers and warehouse providers. It is only a latent growth, because the Hungarian SMEs do not plan to outsource their transport and warehouse activities in a greater extent. The relative high level of logistics as a core competence among processing industry, agriculture and trade SMEs can be a partial explanation to this. The Hungarian small- and medium-sized enterprises face with high logistics costs in international comparison. Its reduction may bring similar savings as reduction of administrative burdens.

„Mennyit ér” a fenntarthatóság? – Esettanulmány az externális hatások mérésére azok internalizálására (What is sustainability worth? – A case study of measuring and internalizing negative environmental effects of logistics operation)

A fenntarthatóság központi kérdés a gazdálkodástudományban, ezen belül a logisztikában, hiszen a környezetre rótt szennyezésben e vállalati működési területnek is jelentős a szerepe. A szerzők dolgozata egy konkrét hazai esettanulmány segítségével vizsgálja a kérdéskört. Azt elemzik, vajon egy, az Európai Unióban is új kamiontípus (az ún. EuroCombi) alkalmazása a logisztikai folyamatokban milyen externális hatásokkal jár. Elemzésükben kísérletet tesznek ezeknek az externális hatásoknak a pénzben kifejezett mérésére. Azért fontos mindez, mert e mérés és számszerűsítés nélkül lehetetlen ezeknek a hatásoknak az internalizálása, vagyis belsővé tétele. Így mérés nélkül sem az érintett vállalatok tulajdonosai, sem azok belső döntéshozói, de a külső szabályozó szereplők sem tudják bevonni e hatásokat gazdasági döntéseikbe. Ez a mérés nem egyszerű feladat, de nem is lehetetlen. Mindenképpen alapját, előfeltételét képezi azonban annak, hogy ilyen jellegű döntéseknél az érintettek a társadalmi, környezeti érdekeket is érvényesíteni tudják. ____ Sustainability is a key issue today both for practitioners and researchers. This is true especially for logisticians. Logistics is a function that has a significant CO2 emission and also destructs transportation infrastructure that burden our environment. The article is focusing on these issues with the help of a Hungarian case study. It analysis the effect of applying a new, long and heavy type of truck, called EuroCombi. It presents a methodology usable for measuring these negative external effects in Forint. Without proper measurement internalization of costs these externalities generate is impossible. As it will be presented in details, such a measurement is although not very easy but achievable.

Electronic Channels of Distributions: Challenges and Solutions for Hotel Operators

This paper addresses the issues of hotel operators identifying effective means of allocating rooms through various electronic channels of distribution. Relying upon the theory of coercive isomorphism, a think tank was constructed to identify and define electronic channels of distribution currently being utilized in the hotel industry. Through two full-day focus groups consisting of key hotel electives and industry practitioners, distribution channels wen identified as were challenges and solutions associated with each

Genetically Altered Foods: A Policy Issue for Multi-unit Food Service Operators

Although it is a substantial issue, the technology behind genetically altered foods and the concerns being raised about them are not well understood by most people. The authors discuss how genetically altered foods might fit into the business strategies of multi-unit food service operators as well as current policies and predispositions of multi-unit food service companies toward the use of genetically altered foods. They also outline the issues surrounding genetically altered food as they relate to the food service industry and provide a picture of where multi-unit food service operators currently stand on the technology

Electronic Channels of Distribution: Challenges and Solutions for Hotel Operators

This paper addresses the issues of hotel operators identifying effective means of allocating rooms through various electronic channels of distribution. Relying upon the theory of coercive isomorphism, a think tank was constructed to identify and define electronic channels of distribution currently being utilized in the hotel industry. Through two full-day focus groups consisting of key hotel executives and industry practitioners, distribution channels were identified as were challenges and solutions associated with each.

The spectra of linear fractional composition operators on weighted Dirichlet spaces

We completely determine the spectra of composition operators induced by linear fractional self-maps of the unit disc acting on weighted Dirichlet spaces; extending earlier results by Higdon [8] and answering the open questions in this context.

Rota’s universal operators and invariant subspaces in Hilbert spaces

A Hilbert space operator is called universal (in the sense of Rota) if every operator on the Hilbert space is similar to a multiple of the restriction of the universal operator to one of its invariant subspaces. We exhibit an analytic Toeplitz operator whose adjoint is universal in the sense of Rota and commutes with a quasi-nilpotent injective compact operator with dense range. In articular, this new universal operator invites an approach to the Invariant Subspace Problem that uses properties of operators that commute with the universal operator.

Geometry of Dirac Operators

Let $M$ be a compact, oriented, even dimensional Riemannian manifold and let $S$ be a Clifford bundle over $M$ with Dirac operator $D$. Then \[ \textsc{Atiyah Singer: } \quad \text{Ind } \mathsf{D}= \int_M \hat{\mathcal{A}}(TM)\wedge \text{ch}(\mathcal{V}) \] where $\mathcal{V} =\text{Hom}_{\mathbb{C}l(TM)}(\slashed{\mathsf{S}},S)$. We prove the above statement with the means of the heat kernel of the heat semigroup $e^{-tD^2}$. The first outstanding result is the McKean-Singer theorem that describes the index in terms of the supertrace of the heat kernel. The trace of heat kernel is obtained from local geometric information. Moreover, if we use the asymptotic expansion of the kernel we will see that in the computation of the index only one term matters. The Berezin formula tells us that the supertrace is nothing but the coefficient of the Clifford top part, and at the end, Getzler calculus enables us to find the integral of these top parts in terms of characteristic classes.

Partner selection for reverse logistics centres in green supply chains: a fuzzy artificial immune optimization approach

The design of reverse logistics networks has now emerged as a major issue for manufacturers, not only in developed countries where legislation and societal pressures are strong, but also in developing countries where the adoption of reverse logistics practices may offer a competitive advantage. This paper presents a new model for partner selection for reverse logistic centres in green supply chains. The model offers three advantages. Firstly, it enables economic, environment, and social factors to be considered simultaneously. Secondly, by integrating fuzzy set theory and artificial immune optimization technology, it enables both quantitative and qualitative criteria to be considered simultaneously throughout the whole decision-making process. Thirdly, it extends the flat criteria structure for partner selection evaluation for reverse logistics centres to the more suitable hierarchy structure. The applicability of the model is demonstrated by means of an empirical application based on data from a Chinese electronic equipment and instruments manufacturing company.

Spectrally isometric elementary operators

We present criteria for unital elementary operators (of small length) on unital semisimple Banach algebras to be spectral isometries. The surjective ones among them turn out to be algebra automorphisms.

More elementary operators that are spectrally bounded

We discuss some necessary and some sufficient conditions for an elementary operator x↦∑ⁿ_i=1a_ixb_i on a Banach algebra A to be spectrally bounded. In the case of length three, we obtain a complete characterisation when A acts irreducibly on a Banach space of dimension greater than three.

Locally quasi-nilpotent elementary operators

Let A be a unital dense algebra of linear mappings on a complex vector space X. Let φ = Σⁿ _i=1 M_ai,_bi be a locally quasi-nilpotent elementary operator of length n on A. We show that, if {a1, . . . , an} is locally linearly independent, then the local dimension of V (φ) = span{b_ia_j : 1 ≤ i, j ≤ n} is at most n(n−1) 2 . If ldim V (φ) = n(n−1) 2 , then there exists a representation of φ as φ = Σⁿ _i=1 M_ui,_vi with v_iu_j = 0 for i ≥ j. Moreover, we give a complete characterization of locally quasinilpotent elementary operators of length 3.

Elementary operators-still not elementary?

Properties of elementary operators, that is, finite sums of two-sided multiplications on a Banach algebra, have been studied under a vast variety of aspects by numerous authors. In this paper we review recent advances in a new direction that seems not to have been explored before: the question when an elementary operator is spectrally bounded or spectrally isometric. As with other investigations, a number of subtleties occur which show that elementary operators are still not elementary to handle.