Assessment of forest community response to environmental variability by using an integrated approach from tree-ring anatomy to allometry of tree structures

Climate change is the biggest challenge of this century and is exerting pressure on high altitude forests. Increase in global temperature along with the rise in CO2 in the atmosphere may change the structure and function of treeline species. Several studies showed the range shifts of trees towards higher altitude affecting growth, mortality, and composition of the forest. There are few studies carried out in Nepalese Himalaya at tree ring level but still miss the inter and intra annual information. To enhance our knowledge, the main objectives of the thesis is to understand the response of treeline species to climate change. This study provides knowledge on the competition between trees for the resources used in the natural forest which alters the structure and pattern of the forest ecosystem. The target species for wood anatomical and isotopic study were Abies spectabilis D. Don Mirb. and Betula utilis D. Don which is dominating in upper treeline of Himalayas. I used the dendro-anatomy to assess the growth responses of xylem anatomical traits to climatic constraints. This allowed retrieving the information at a cellular level with longer time resolution. Further, the results were complemented by isotopic measurements that were inscribed in wood cellulose during their formation. Moreover, dendrometric data (DBH, crown radius, tree height) were collected from forest permanent plots located from different geographic locations (Nepal, Italy, and Romania). The data were used to test the crown allometries and their effects on natural forest structure and dynamics using crown area and crown volume models. Wood anatomical studies of B. utilis showed mean ring width, mean vessel area, and ring specific hydraulic conductivity to positively correlated with summer temperatures. However, fibers were negatively correlated with same season temperature suggesting that fiber get narrower when the vessel is wider to maintain the xylem hydraulic system. Another, study based on dual isotope (carbon and oxygen) showed growing season water availability could be a supplementary limiting factor for this treeline species though high altitude species are mainly limited by low temperature. In such a condition, A. spectabilis, a high altitude conifer could benefit from its higher water use efficiency during the drier period taking the competitive advantage to gas exchange compare to B. utilis. The last part of a study on the crown geometry of natural forest showed trees are site-specific determining the structure of forest ecosystem through growth, mortality, and recruitment. The predicted number of trees calculated based on crown area/volume models suggested that natural forest is oriented towards a condition of space equivalence between tree-size classes, showing in parallel that the use of soil resources increment in higher tree classes. In conclusion, this thesis provides information on wood anatomy and physiology of treeline species in response to global warming. Integration of crown models opens the idea how crown allometries contribute to a better understanding of forest communities and dynamics

Properties of unique hard X-ray dips observed from GRS 1915+105 and IGR J17091-3624 and their implications

We report a comprehensive study on spectral and timing properties of hard X-ray dips uniquely observed in some so-called variability classes of the micro-quasars GRS 1915+105 and IGR J17091-3624. These dips are characterized by a sudden decline in the 2.0-60.0 keV X-ray intensity by a factor of 4-12 simultaneous with the increase in hardness ratio by a factor of 2-4. Using 31 observations of GRS 1915+105 with RXTE/PCA, we show that different behavior are observed in different types of variability classes, and we find that a dichotomy is observed between classes with abrupt transitions vs those with smoother evolution. For example, both energy-lag spectra and frequency-lag spectra of hard X-ray dips in classes with abrupt transitions and shorter dip intervals show hard-lag (hard photons lag soft photons), while both lag spectra during hard dips in classes with smoother evolution and longer dip intervals show soft-lag. Both lag time-scales are of the order of 100-600 msec. We also show that timing and spectral properties of hard X-ray dips observed in light curves of IGR J17091-3624 during its 2011 outburst are consistent with the properties of the abrupt transitions in GRS 1915+105 rather than smooth evolution. A global correlation between the X-ray intensity cycle time and hard dip time is observed for both abrupt and smooth transition which may be due to two distinct physical processes whose time-scales are eventually correlated. We discuss implications of our results in the light of some generic models.Comment: 17 pages, 5 figures, accepted for publication in the Astrophysical Journa

Modified celestial amplitude in Einstein gravity

In this paper we evaluate the modified celestial amplitude for gravitons and gluons, as defined in [4]. We find that the modified (tree) amplitude is finite for gravitons in Einstein gravity. The modified amplitude behaves like correlation function of operators inserted at various points of null-infinity in the Minkowski space-time. Therefore, unlike the standard celestial amplitudes, these are three dimensional objects. We also show that this amplitude admits conformal soft factorization recently studied in the literature

crop protection and its effectiveness against wildlife a case study of two villages of shivapuri national park nepal

A complex relationship between the residents and protected areas continue to be an obstacle to successful conservation of protected areas. Conflicts between park authority and people living around the park pose a threat to conservation. Moreover, crop depredation due to wildlife incurs a severe economic loss to communities living in the close vicinity of the park, affecting the livelihood and well-being of locals. Many studies have been carried out emphasizing the identification and quantification of crop damage, but studies highlighting the means used for the crop protection and their effectiveness are limited. This paper examines frequency of the crop damage by wildlife and efficacy of utilized management practices in Shivapuri National Park (SNP). Altogether 132 households were visited in two buffer zone villages namely, Sikre and Jhor Mahankhal of Shivapuri National Park, Nepal. The study suggested that crop depredation by wildlife was a function of several factors, namely, distance of the farmland from the park, size of the crop raiding animals, frequency of their attacks on the farmland, and the type of crops. Five different measures were identified by the communities which they regularly used to prevent crop damage. Both traditional as well as modern means were used by households to guard crops from invading wild animals. The means of crop protection from wildlife differed according to the type of animal and crop being protected. Biofencing and trenches were effective for the small animals. Watch tower "Machans" and throwing flaming sticks and making noises were the most effective and safest means of crop guarding from all kind of animals. Though crop guarding was intensive, no means were found to be able to prevent crop damage completely. Thus, site specific management strategies as well as technical and financial support from donor organizations would be most useful to minimize crop loss.Nepal Journal of Science and Technology Vol. 16, No.1 (2015) pp. 1-1

Phase Transitions and Magnetocaloric Properties in MnCo1- xZrxGe Compounds

The structural, magnetic, and magnetocaloric properties of MnCo1-xZrxGe (0.01≤x≤0.04) have been studied through X-ray diffraction, differential scanning calorimetry, and magnetization measurements. Results indicate that the partial substitution of Zr for Co in MnCo1-xZrxGe decreases the martensitic transition temperature (TM). For x = 0.02, TM was found to coincide with the ferromagnetic transition temperature (TC) resulting in a first-order magnetostructural transition (MST). A further increase in zirconium concentration (x = 0.04) showed a single transition at TC. The MST from the paramagnetic to ferromagnetic state results in magnetic entropy changes (-ΔSM) of 7.2 J/kgK for ΔH = 5 T at 274 K for x = 0.02. The corresponding value of the relative cooling power (RCP) was found to be 266 J/kg for ΔH = 5 T. The observed large value of MCE and RCP makes this system a promising material for magnetic cooling applications

Effects of Rare-Earth (R = Pr, Gd, Ho, Er) Doping on Magnetostructural Phase Transitions and Magnetocaloric Properties in Ni43-xRxMn46Sn11 Shape Memory Alloys

A series of rare-earth-doped Ni43-xRxMn46Sn11 (x= 0, 1 and R = Pr, Gd, Ho, Er) alloys was fabricated by arc melting, and their structural, magnetic, and magnetocaloric properties were studied through room temperature X-ray diffraction (XRD), differential scanning calorimetry, and magnetization measurements. Analysis of XRD data reveal that the alloys crystallize in the cubic L21 austenite phase structure as the major phase with a small trace of martensitic phase (MP). The martensitic transition temperature (TM) shifts to consecutive higher temperatures with the substitution of Pr, Gd, Ho, and Er. A drastic shift in TM by 60 K relative to the parent compound (TM= 195 K) was found for Ni42PrMn46Sn11. Large values of magnetic entropy changes (Δ SM) of 32 (Pr), 28 (Gd), and 25Jkg-1K-1 (Ho) were obtained at TM for Δ H = 50 kOe. A maximum value of the refrigeration capacity of ∼ 250Jkg-1 was obtained in the vicinity of TM for Δ H=50 kOe for the Ho-doped compound. A large exchange bias effect with HEB ∼ 1.1 kOe at 10 K was observed for the Pr-doped compound in its MP

Evidence of two unique variability classes from IGR J17091-3624

IGR J17091-3624 is the second black hole X-ray binary after GRS 1915+105, which showed large and distinct variabilities. The study of these variability classes can be useful to understand the accretion-ejection mechanisms of accreting black holes, and hence to probe the strong gravity regime. We report the discovery of two new variability classes (C1 and C2) from IGR J17091-3624 from the 2011 outburst Rossi X-ray Timing Explorer data. These unique classes will be useful to have complete details about the source, and to learn new aspects about variabilities. For examples, the C1 class shows that the intensity and period of oscillations, energy spectrum and power spectrum can clearly evolve in tens of seconds. Moreover, in such a small time scale, soft-lag becomes hard-lag. The C2 class shows that the variability and the nonvariability can occur at similar energy spectrum, and a soft state is not required for variability to happen.Comment: 5 pages, 6 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society Letter

Magnetic, structural and magnetocaloric properties of Ni-Si and Ni-Al thermoseeds for self-controlled hyperthermia

Self-controlled hyperthermia is a non-invasive technique used to kill or destroy cancer cells while preserving normal surrounding tissues. We have explored bulk magnetic Ni-Si and Ni-Al alloys as a potential thermoseeds. The structural, magnetic and magnetocaloric properties of the samples were investigated, including saturation magnetisation, Curie temperature (TC), and magnetic and thermal hysteresis, using room temperature X-ray diffraction and magnetometry. The annealing time, temperature and the effects of homogenising the thermoseeds were studied to determine the functional hyperthermia applications. The bulk Ni-Si and Ni-Al binary alloys have Curie temperatures in the desired range, 316 K–319 K (43 °C–46 °C), which is suitable for magnetic hyperthermia applications. We have found that TC strictly follows a linear trend with doping concentration over a wide range of temperature. The magnetic ordering temperature and the magnetic properties can be controlled through substitution in these binary alloys

Large inverse magnetocaloric effects and giant magnetoresistance in Ni-Mn-Cr-Sn heusler alloys

The magnetostructural transitions, magnetocaloric effects, and magnetoresistance properties of Ni45Mn43CrSn11 Heusler alloys were investigated using X-ray diffraction (XRD), field-dependent magnetization, and electrical resistivity measurements. A large inverse and direct magnetocaloric effect has been observed in Ni45Mn43CrSn11 across the martensitic and Curie transition temperature, respectively. The values of the latent heat (L = 15.5 J/g) and corresponding magnetic (∆SM) and total (∆ST) entropy changes (∆SM = 35 J/kg·K for ∆H = 5T and ∆ST = 39.7 J/kg·K) have been evaluated using magnetic and differential scanning calorimetry (DSC) measurements, respectively. A substantial jump in resistivity was observed across the martensitic transformation. A large negative magnetoresistance (~67%) was obtained at the magnetostructural transition for a field change of 5 T. The roles of the magnetic and structural changes on the transition temperatures and the potential application of Ni45Mn43CrSn11 Heusler alloys for refrigerator technology are discussed