The temperature dependent lattice thermal conductivity (κph) of MAX phases, Mn+1AXn are calculated using the Debye theory as outlined by Slack. At high temperature the formula derived by Slack is a ...reasonable approximation to estimate the lattice thermal conductivity. The calculation used the large data base of elastic coefficients of stable MAX phases established recently. It is found that MAX phases with “A”=Al have higher κph at 1300K, and the majority of MAX carbides have higher κph than MAX nitrides. We have also calculated the minimum thermal conductivities of these MAX phases using the empirical formula suggested by Clarke. It is shown that the minimal lattice thermal conductivities of MAX carbides and nitrides are closer to each other in the 211 phases than in higher n phases. The calculated κph for 8 MAX phases at 1300K are in reasonable agreement with experimental data, especially in Ti2AlC, Nb4AlC3, Ta4AlC3, Nb2AlC and Nb2SnC phases.
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In this study, we report a comprehensive assessment on the elastic and electronic properties of 792 possible MAX (Mn+1AXn) phases with n = 1–4 using ab initio methods. These crystals are then ...screened based on their elastic and thermodynamic stability resulting in a large database of 665 viable crystals. All the experimentally verified MAX phases passed the screening. Various correlations among and between them are fully explored. In particular, the key elements in the interdependence between the elastic properties together with mechanical parameter derived from them and the electronic structure are identified. Detailed analysis of various correlation plots shows that there is a clear correspondence between bulk modulus K and total bond order density (TBOD). Calculations show a marked difference between the carbides and nitrides. This database is also used to test the efficacy of data mining algorithms for materials genome. We further identified several thermodynamically stable new MAX phases with unusual mechanical parameters that have never been synthesized in the laboratory or theoretically investigated. The complete database on the elastic and electronic structure together with the mechanical parameters for these 665 MAX phases compounds are included in the Supplementary Materials and fully accessible.
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Background
The tobacco cutworm,
Spodoptera litura
Fab. (Lepidoptera: Noctuidae), is a devastating insect pest of several crops. Entomopathogenic nematodes (EPNs) of the families Heterorhabditidae and ...Steinernematidae are used as an alternative control measure in lieu of the hazardous synthetic chemical applications.
Results
A survey of naturally occurring EPNs was conducted across the province of Cotabato, Philippines, covering a total of 5 municipalities with 25 villages.
Galleria
-baiting technique was employed to recover nematodes from peanut and grassland soils. Out of 50 soil samples collected, only 5 samples harbored nematodes, indicating a recovery of 10%. Preliminary morphological data identified only one EPN under the genera
Heterorhabditis
(1 isolate), whereas 4 were facultative necromenic nematodes from the genera
Metarhabditis
(2 isolates) and
Oscheius
(2 isolates). Analysis of D2D3 segments of the 28S rDNA confirmed high sequence similarity to
Heterorhabditis indica
,
Metarhabditis rainai
,
Oscheius insectivora
, and
Oscheius
sp. This is the first record of
H. indica
and
M. rainai
in the entire region, whereas the first record for
Oscheius
spp. in the Philippines. Furthermore, the biocontrol potential of the local
H. indica
infective juvenile (IJ) populations (PIGCD1) isolated from peanut was assessed against the tobacco cutworm,
S. litura
, under laboratory conditions. The mean percentage mortality caused by
H. indica
on
S. litura
at 7 different concentrations ranged from 0-100% at 24 h post inoculation. The lethal concentration (LC
50
) required to kill 50% of the
S. litura
larvae population with
H. indica
was 7.13±1 (IJs/larva).
Conclusions
The use of
Galleria
-baiting method is a convenient approach to detect EPNs including other facultative necromenic nematodes from the soils. Obtained data indicated that the local
H. indica
isolate can be a promising alternative measure to suppress the economically important insect pest,
S. litura
, and this may provide significant outlook to establish the biocontrol program in the country.
Background
Entomopathogenic nematodes (EPNs) of the families Heterorhabditidae and Steinernematidae are used as biological control agents of several insect pests in lieu of synthetic pesticides.
...Results
Using an insect-baiting technique, naturally occurring EPN isolates were collected from banana and rice fields in the municipality of Hagonoy, the Philippines. A total of 4 isolates were recovered from all the sites namely, HBP1, HBP2, HR3 and HR4. By combining morphometrical and ITS rDNA data, all the isolates were identified as
Heterorhabditis indica
. To initially assess their infectivity, virulence tests were conducted on the last instar larvae of the super worm,
Zophobas morio
Fabricius (Coleoptera: Tenebrionidae), the model insect. HR3 isolate had the highest percentage mortality (56%), followed by HBP1 and HBP2 (33%), which were comparable to the available nematode in the market,
Heterorhabditis bacteriophora
(44%), whereas the lowest was obtained in HR4 isolate (11%).
Conclusions
This study accounted 4 more
H
.
indica
isolates in addition to pre-existing isolates in the country, expanding its habitat range and geographic distribution. This also provides baseline information on the potential biocontrol utilization of native EPNs against soil-dwelling insect pests of agricultural crops. Further investigations are required to assess their efficacy against several other insect pests of economic importance for the integrated pest management (IPM) programmes in the country.
Background
Entomopathogenic nematodes of the genera
Heterorhabditis
and
Steinernema
are widely used as biocontrol agents against diverse insect pests. Their association with symbiont bacteria is ...found to be the primary cause of insect mortality. The present study reported a comprehensive characterization of a local Philippine EPN isolate using congruent morpho-taxometrical and molecular data and the associated bacterium in the infective dauer juveniles.
Results
Using an insect-baiting technique, a nematode isolate labeled F2H was recovered from the sandy soils in the coastal area of southern Philippines. Based on morphology and morpho-taxometrics, the F2H isolate collected from Iligan City was identified as
Heterorhabditis indica
. Analysis of the ITS region of rDNA revealed the highest sequence match to
H. indica
. The sequences of the bacterial 16S rDNA gene showed that the symbiont of
H. indica
presented 100% similitude with the sequences of
Ochrobactrum anthropi
. Further, pairwise alignment and phylogenetic analysis demonstrated that
O. anthropi
,
O. lupini
and
O. cytisi
shared 100% similarity and form a monophyletic clade. These strains have not presented any differences in the phylogenetic and 16S rDNA data, and
O. lupini
and
O. cytisi
should be considered a later heterotypic synonym of
O. anthropi
.
Conclusions
The description of
H. indica
-
O. anthropi
association was the first report in the Philippines. This provides additional account and collection of naturally isolated EPN-bacteria, contributing to limited knowledge on its diversity in the Philippines, which can be utilized in the biocontrol of pests after further comprehensive assessments.
A study on reproductive disorders among yaks in Mustang and Solukhumbu districts and seroprevalence of brucellosis among yaks in Mustang and Myagdi districts was conducted. Eleven farmers having 383 ...female and 72 male yaks in Mustang and 129 female and 27 male yaks in Solukhumbu districts were taken by purposive random sampling for the study on reproductive disorders. Likewise Sixty-seven serum samples were also collected from adult female yaks having history of abortion and retained placenta, and from male yaks used for breeding purpose from Mustang and Myagdi districts. An average of 12.63% of female yaks aborted, 7.26% had had retention of placenta and 6.6% repeat breeders in Mustang district. Similarly, 6.3% had abortion, 2.09% retained placenta and 6.5% repeat breeders in Solukhumbu district. However, all the 67 serum samples examined were found negative to the Brucella abortus antibody on ELISA test suggesting that the yak population was free from brucellosis in these areas. Thus abortion and retention of placenta in Yak in Mustang district may not be due to brucellosis. A detail study should be done to find the specific cause of abortion and repeat breeding to recommend preventive and control measures.Nepal Agric. Res. J. Vol. 8, 2007, pp. 130-132 DOI: http://dx.doi.org/10.3126/narj.v8i0.11608
We have investigated the mechanism of densification of a nearly perfect continuous random network (CRN) model of amorphous SiO
2
(a-SiO
2
) glass with 1296 atoms and periodic boundary conditions. The ...model has no under- or over-coordinated atoms and small bond length and bond angle distributions. This near-perfect model is systematically densified up to a pressure of 80 GPa using
ab initio
constant-pressure technique. By assessing a full spectrum of properties including atomic structure, bonding characteristics, effective charges, bond order values, electron density of states, localization of wave functions, elastic and mechanical properties, and interband optical absorption at each pressure, we reveal the pertinent details on the structural, mechanical and optical characteristics of the glass model under pressure. They all confirm the central theme that amorphous to amorphous phase transformation (AAPT) from a low-density state to a high-density state is at a pressure between 20 and 35 GPa in this nearly ideal a-SiO
2
network. This pressure range represents an upper limit for such a transition in vitreous silica. The phase transformation roots from the change of Si-O bonding from a mixture of ionic and covalent nature at low pressure to a highly covalent bonding under high pressure. In addition, the calculated theoretical refractive index of the glass model as a function of the pressure is reported for the first time and in good agreement with the available experimental data.
This study provides a comprehensive understanding on how the structure is related to the physical and electronic properties of dense silica glass.
•Comprehensive study of 36 Australian EPN strains.•All EPN strains infected and killed larvae of Bactrocera tryoni.•Most EPN strains (84%) also caused pupal mortality.•EPN strain baited with B. ...tryoni was virulent against both developmental stages.•Seven EPN strains are promising candidates to control B. tryoni.
Queensland fruit fly (Bactrocera tryoni) is Australia’s most significant horticultural pest, yet limited options are available for its biological control. Here, we assessed the virulence and reproductive potential of 32 newly isolated Australian entomopathogenic nematode (EPN) strains of Heterorhabditis bacteriophora, Heterorhabditis indica, Heterorhabditis marelatus, Heterorhabditis zealandica and Steinernema feltiae against the late third larval instar and pupal stages of B. tryoni under laboratory conditions, and compared their performance with four commercially available strains of H. bacteriophora, H. zealandica, S. feltiae and S. carpocapsae. All EPN strains caused significant larval mortality, and, remarkably, 29 also pupal mortality. Among the EPN strains the mean LD50 value, presented as the number of infective juveniles (IJs) per B. tryoni individual, ranged from 25 to 114 IJs per larva, and from 114 to 360 per pupa; therefore, 3.2 to 4.6× more IJs were required to kill pupae. The penetration rates of IJs in B. tryoni larvae varied from 2 to 6.8%, and the number of IJs recovered per larva varied between 2,100 to 5,683. Our findings highlight the potential of Australian EPN strains for controlling larval and pupal stages of B. tryoni. Overall, based on the three tested traits, one H. zealandica strain (Hz.NAR1), three H. indica strains (Hi.ECCH, Hi.HRN and Hi.HIE2), one H. bacteriophora strain (Hb.HIE), one H. marelatus strain (Hm.ENCBF2) and one S. feltiae strain (Sf.Y13) were found the most promising candidates as potential biological control agents against the soil inhabiting stages of B. tryoni. Further laboratory testing is required to assess their persistence under a broader range of environmental conditions before their biological control efficacy can be trialled under field conditions.
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The intrinsic mechanical properties of 20 MAX‐phase compounds are calculated using an ab initio method based on density functional theory. A stress versus strain approach is used to obtain the ...elastic coefficients and thereby obtain the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio based on the Voigt–Reuss–Hill (VRH) approximation for polycrystals. The results are in good agreement with available experimental data. It is shown that there is an inverse correlation between Poisson's ratio and the Pugh ratio of shear modulus to bulk modulus in MAX phases. Our calculations also indicate that two MAX compounds, Ti2AsC and Ti2PC, show much higher ductility than the other compounds. It is concluded that the MAX‐phase compounds have a wide range of mechanical properties ranging from very ductile to brittle with the “A” in the MAX phase being the most important controlling element. The measured Vickers hardness in MAX compounds has no apparent correlation with any of the calculated mechanical parameters or their combinations.
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