Gravity waves and instabilities in the lower and middle atmosphere

Some basic aspects of mesoscale and small-scale gravity waves and instability mechanisms are discussed. Internal gravity waves with wavelengths between ten and less than one kilometer and periods between several hours and several minutes appear to play a central role in atmospheric wavenumber and frequency spectra. Therefore, the author discusses the propagation of gravity waves in simplified atmospheric models. Their interaction with the wind as well as their mutual interaction and stability mechanisms based on these processes are discussed. Mesosphere stratosphere troposphere radar observations showing the relevant hydrodynamic processes are stressed

Protecting a Graph with Mobile Guards

Mobile guards on the vertices of a graph are used to defend it against attacks on either its vertices or its edges. Various models for this problem have been proposed. In this survey we describe a number of these models with particular attention to the case when the attack sequence is infinitely long and the guards must induce some particular configuration before each attack, such as a dominating set or a vertex cover. Results from the literature concerning the number of guards needed to successfully defend a graph in each of these problems are surveyed.Comment: 29 pages, two figures, surve

Disjoint Dominating Sets with a Perfect Matching

In this paper, we consider dominating sets $D$ and $D'$ such that $D$ and $D'$ are disjoint and there exists a perfect matching between them. Let $DD_{\textrm{m}}(G)$ denote the cardinality of smallest such sets $D, D'$ in $G$ (provided they exist, otherwise $DD_{\textrm{m}}(G) = \infty$). This concept was introduced in [Klostermeyer et al., Theory and Application of Graphs, 2017] in the context of studying a certain graph protection problem. We characterize the trees $T$ for which $DD_{\textrm{m}}(T)$ equals a certain graph protection parameter and for which $DD_{\textrm{m}}(T) = \alpha(T)$, where $\alpha(G)$ is the independence number of $G$. We also further study this parameter in graph products, e.g., by giving bounds for grid graphs, and in graphs of small independence number

The Eternal Game Chromatic Number of a Graph

Game coloring is a well-studied two-player game in which each player properly colors one vertex of a graph at a time until all the vertices are colored. An `eternal' version of game coloring is introduced in this paper in which the vertices are colored and re-colored from a color set over a sequence of rounds. In a given round, each vertex is colored, or re-colored, once, so that a proper coloring is maintained. Player 1 wants to maintain a proper coloring forever, while player 2 wants to force the coloring process to fail. The eternal game chromatic number of a graph $G$ is defined to be the minimum number of colors needed in the color set so that player 1 can always win the game on $G$. We consider several variations of this new game and show its behavior on some elementary classes of graphs

Department of Entomology Newsletter, University of Nebraska, No. 4 -- 1976

The Newsletter Committee has succeeded in documenting departmental activities in an outstanding manner. All of us in the department appreciate the wonderful efforts and many hours spent by the Newsletter Committee: Brett Ratcliffe, Ron Rivers, Bruce Monke, Tim Miller and particularly the leadership of Lyle Klostermeyer as Committee Chairman. The typing assistance of our secretarial staff is greatly appreciated. The many changes in personnel and programs that have taken place during the period since the 1968 publication of Departmental Newsletter No.3 are well covered in various sections of the newsletter. We also compliment the Committee on their choice of dedicating this issue to Roscoe Hill and Sally Schock, two people well known to all receiving the Newsletter. Thank you for your participation in responding to the Committee\u27s questionnaire, and we look forward to all of you visiting the department. We particularly welcome you to visit the campus and the department during the April 23, 1977 meeting of the Central States Entomological Society under the leadership of Roscoe Hill, 1976-77 President. Looking ahead, we will also be hosting the 1980 meeting of the North Central Branch of the Entomological Society of America in Lincoln. Best wishes to all former associates of the department and we hope you enjoy Departmental News~etter No.4. ELVIS A. DICKASON Chairman (1970 - ) PLANT INDUSTRY FIRE A phone calI in the early hours of Friday, August 22, 1975 was the start of a very traumatic and tiring experience for the occupants of the Plant Industry Bui Iding (PI) on the East Campus of the University of Nebraska. MYRON H. SWENK MEMORIAL FUND BRUNER ENTOMOLOGY CLUB OCCUPATION OUTLOOK SYMPOSIUM CAMPUS CHANGES Since the Last Newsletter ENTOMOLOGY MUSEUM FIELD TRIPS NEvv HALLWAY DISPLAYS TUMBLEBUGS DEPARTMENT CHAIRMEN LAWRENCE BRUNER 1888 - 1919 H. DOUGLAS TATE 1941 - 1946 ROSCOE E. HILL 1950 - 1966 MYRON H. SWENK 1919 - 1941 EPHRIAM HIXSON 1946 -1950 EARLE S. RAUN 1966 - 1970 Some Nebraska Entomological History Compiled by Roscoe HiII NEW FACULTY SINCE 1968 Wa lter J. Gary Thomas Holtzer Z B Mayo Leroy L. Peters Brett C. Ratcliffe John F. Witkowski FACULTY Lloyd W. Andersen Harold J. Ball Jerold H.L. Bell John B. Campbell Arthur Hagen Thomas J. Helms David L. Keith Dean Kindler George R. Manglitz Kenneth P. Pruess Robert E. Roselle Robert Staples SUPPORT PERSONNEL Frank J. Basel James F. Brown Terry Bruce Terry Dukes Marcia Fuhrer Nina Jeffrey Timothy P. Miller Rosemarie Moats Connie Pol icky Jan Radenslaben Henry Stevens Paulina Su GRADUATE STUDENTS James Ballard Gary Brewer Don Carpino Lyle E. Klostermeyer Albert Lew Bruce Monke Jones Mueke James P. Newton Rebecca Rasmussen Robert M. Roselle Jack Shugart Ronnie Rivers Alumni Publications (80 pp

Eternal Independent Sets in Graphs

The use of mobile guards to protect a graph has received much attention in the literature of late in the form of eternal dominating sets, eternal vertex covers and other models of graph protection. In this paper, eternal independent sets are introduced. These are independent sets such that the following can be iterated forever: a vertex in the independent set can be replaced with a neighboring vertex and the resulting set is independent

Vertex covers and eternal dominating sets

AbstractThe eternal domination problem requires a graph to be protected against an infinitely long sequence of attacks on vertices by guards located at vertices, the configuration of guards inducing a dominating set at all times. An attack at a vertex with no guard is defended by sending a guard from a neighboring vertex to the attacked vertex. We allow any number of guards to move to neighboring vertices at the same time in response to an attack. We compare the eternal domination number with the vertex cover number of a graph. One of our main results is that the eternal domination number is less than the vertex cover number of any graph of minimum degree at least two having girth at least nine