A Comparison between the Zero Forcing Number and the Strong Metric Dimension of Graphs

The \emph{zero forcing number}, $Z(G)$, of a graph $G$ is the minimum cardinality of a set $S$ of black vertices (whereas vertices in $V(G)-S$ are colored white) such that $V(G)$ is turned black after finitely many applications of "the color-change rule": a white vertex is converted black if it is the only white neighbor of a black vertex. The \emph{strong metric dimension}, $sdim(G)$, of a graph $G$ is the minimum among cardinalities of all strong resolving sets: $W \subseteq V(G)$ is a \emph{strong resolving set} of $G$ if for any $u, v \in V(G)$, there exists an $x \in W$ such that either $u$ lies on an $x-v$ geodesic or $v$ lies on an $x-u$ geodesic. In this paper, we prove that $Z(G) \le sdim(G)+3r(G)$ for a connected graph $G$, where $r(G)$ is the cycle rank of $G$. Further, we prove the sharp bound $Z(G) \leq sdim(G)$ when $G$ is a tree or a unicyclic graph, and we characterize trees $T$ attaining $Z(T)=sdim(T)$. It is easy to see that $sdim(T+e)-sdim(T)$ can be arbitrarily large for a tree $T$; we prove that $sdim(T+e) \ge sdim(T)-2$ and show that the bound is sharp.Comment: 8 pages, 5 figure

Is CH3NH3PbI3 Polar?

In view of the continued controversy concerning the polar/nonpolar nature of the hybrid perovskite system, CH3NH3PbI3, we report the first investigation of a time resolved pump probe measurement of the second harmonic generation efficiency as well as using its more traditional form as a sensitive probe of the absence/presence of the center of inversion in the system both in its excited and ground states, respectively. Our results clearly show that SHG efficiency, if nonzero, is below the limit of detection, strongly indicative of a nonpolar or centrosymmetric structure. Our results on the same samples, based on temperature dependent single crystal X-ray diffraction and P-E loop measurements, are entirely consistent with the above conclusion of a centrosymmetric structure for this compound in all three phases, namely the high temperature cubic phase, the intermediate temperature tetragonal phase and the low temperature orthorhombic phase. It is important to note that all our experimental probes are volume averaging and performed on bulk materials, suggesting that basic material properties of CH3NH3PbI3 are consistent with a centrosymmetric, nonpolar structure

Incorporating Carbon Storage into the Optimal Management of Forest Insect Pests: A Case Study of the Southern Pine Beetle (Dendroctonus Frontalis Zimmerman) in the New Jersey Pinelands

Forest insect pest disturbance is increasing in certain areas of North America as many insect species, such as the southern pine beetle, expand their range due to a warming climate. Because insect pests are beginning to occupy forests that are managed for multiple uses and have not been managed for pests before, it is becoming increasingly important to determine how forests should be managed for pests when non-timber ecosystem services are considered in addition to traditional costs and revenues. One example of a service that is increasingly considered in forest management and that may affect forest pest management is carbon sequestration. This manuscript seeks to understand whether the incorporation of forest carbon sequestration into cost-benefit analysis of different forest pest management strategies affects the financially optimal strategy. We examine this question through a case study of the southern pine beetle (SPB) in a new area of SPB expansion, the New Jersey Pinelands National Reserve (NJPR). We utilize a forest ecology and economics model and include field data from the NJPR as well as outbreak probability statistics from previous years. We find under the majority of scenarios, incorporating forest carbon sequestration shifts the financially optimal SPB management strategy from preventative thinning toward no management or reactionary management in forest stands in New Jersey. These results contradict the current recommended treatment strategy for SPB and signify that the inclusion of multiple ecosystem services into a cost-benefit analysis may drastically alter which pest management strategy is economically optimal

Ionospheric Response to Natural and Man Made Impacts

International audienceThe problem of energy transfer from the Earth’s solid mantles to the atmosphere and surrounding space is of essential importance for the fundamental geophysics and applied studies. These processes can largely govern the structure and dynamics of the phenomena developing in the near Earth space. Moreover, the consequences of such impacts as earthquakes, hurricanes, etc. upon the Earth’s electromagnetic field and ionosphere can become an extra factor in monitoring the processes involved in the upcoming large-scale seismic and meteorological catastrophes. The acoustic-gravity waves (comprising acoustic and gravity waves and hereafter referred to as AGW) are one of the most efficient ways to transport over the ionosphere the energy of the dynamic processes developing in the low atmosphere. The early experiments of the 1950’s and 60’s on Doppler sounding even showed that the ionosphere can serve as a sensitive indicator of natural and man made disturbances. The Doppler sounding of the ionosphere revealed impulse and wave disturbances excited by powerful sources of infrasound, such as: a) megaton nuclear explosions in the atmosphere, kiloton ground industrial explosions, b) earthquakes and volcano eruptions, c) thunderstorms, tornadoes and tsunamis, d) bolides and meteorites, e) rocket launches and flights of supersonicjets, f) aurora and solar eclipse