Bounds for the Laplacian Spectral Radius of Graphs

This paper is a survey on the upper and lower bounds for the largest eigenvalue of the Laplacian matrix, known as the Laplacian spectral radius, of a graph. The bounds are given as functions of graph parameters like the number of vertices, the number of edges, degree sequence, average 2-degrees, diameter, covering number, domination number, independence number and other parameters

Behavior and Impact of Zirconium in the Soil–Plant System: Plant Uptake and Phytotoxicity

Because of the large number of sites they pollute, toxic metals that contaminate terrestrial ecosystems are increasingly of environmental and sanitary concern (Uzu et al. 2010, 2011; Shahid et al. 2011a, b, 2012a). Among such metals is zirconium (Zr), which has the atomic number 40 and is a transition metal that resembles titanium in physical and chemical properties (Zaccone et al. 2008). Zr is widely used in many chemical industry processes and in nuclear reactors (Sandoval et al. 2011; Kamal et al. 2011), owing to its useful properties like hardness, corrosion-resistance and permeable to neutrons (Mushtaq 2012). Hence, the recent increased use of Zr by industry, and the occurrence of the Chernobyl and Fukashima catastrophe have enhanced environmental levels in soil and waters (Yirchenko and Agapkina 1993; Mosulishvili et al. 1994 ; Kruglov et al. 1996)

Accumulated hippocampal formaldehyde induces age-dependent memory decline

Aging is an important factor in memory decline in aged animals and humans and in Alzheimer's disease and is associated with the impairment of hippocampal long-term potentiation (LTP) and down-regulation of NR1/NR2B expression. Gaseous formaldehyde exposure is known to induce animal memory loss and human cognitive decline; however, it is unclear whether the concentrations of endogenous formaldehyde are elevated in the hippocampus and how excess formaldehyde affects LTP and memory formation during the aging process. In the present study, we report that hippocampal formaldehyde accumulated in memory-deteriorating diseases such as age-related dementia. Spatial memory performance was gradually impaired in normal Sprague-Dawley rats by persistent intraperitoneal injection with formaldehyde. Furthermore, excess formaldehyde treatment suppressed the hippocampal LTP formation by blocking N-methyl-d-aspartate (NMDA) receptor. Chronic excess formaldehyde treatment over a period of 30 days markedly decreased the viability of the hippocampus and down-regulated the expression of the NR1 and NR2B subunits of the NMDA receptor. Our results indicate that excess endogenous formaldehyde is a critical factor in memory loss in age-related memory-deteriorating diseases