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Fig. 7 in Taxonomic revaluation of the Ahaetulla prasina (H. Boie in F. Boie, 1827) complex from Northeast India: resurrection and redescription of Ahaetulla flavescens (Wall, 1910) (Reptilia: Serpentes: Colubridae)

Fig. 7. Ahaetulla flavescens (Wall, 1910) comb. nov. Live uncollected specimens from Arunachal Pradesh, showing the unusual buff or yellowish-brown colouration. Photo: Bharat Bhushan Bhatt.

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Fig. 6. Dryophis prasinusvar. flavescens Wall, 1910 in Taxonomic revaluation of the Ahaetulla prasina (H. Boie in F. Boie, 1827) complex from Northeast India: resurrection and redescription of Ahaetulla flavescens (Wall, 1910) (Reptilia: Serpentes: Colubridae)

Fig. 6. Dryophis prasinusvar. flavescens Wall, 1910, lectotype (NHMUK 1908.6.23.58) and paralectotype (NHMUK 1908.6.23.59). Jar label. Photo: ©The Trustees of the Natural History Museum, London.

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Fig. 5. Dryophis prasinus var. flavescens Wall, 1910 in Taxonomic revaluation of the Ahaetulla prasina (H. Boie in F. Boie, 1827) complex from Northeast India: resurrection and redescription of Ahaetulla flavescens (Wall, 1910) (Reptilia: Serpentes: Colubridae)

Fig. 5. Dryophis prasinus var. flavescens Wall, 1910, lectotype (NHMUK 1908.6.23.58). Head close-up showing the divided 4th supralabial on right side, a unique identifying character in ascertaining its type status. Photo: ©The Trustees of the Natural History Museum, London.

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Fig. 2 in Taxonomic revaluation of the Ahaetulla prasina (H. Boie in F. Boie, 1827) complex from Northeast India: resurrection and redescription of Ahaetulla flavescens (Wall, 1910) (Reptilia: Serpentes: Colubridae)

Fig. 2. The bPTP output trees generated from three mitochondrial loci ML trees. Blue coloured branches and black bars indicate monophyly of that lineage, where validity of lineages is further ascertained with genetic divergence (genetic p-distance) and geographic isolation. The grey bars indicate the genetic distance (G1) and geographic isolation (G2) among lineages. The values on clades indicate the posterior probability. The A. prasina complex (Lineage 1 and Lineage 2) from northeast India shows a very low genetic divergence with continuous geographic distribution.

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Fig. 3. Dryophis prasinus var. flavescens Wall, 1910 in Taxonomic revaluation of the Ahaetulla prasina (H. Boie in F. Boie, 1827) complex from Northeast India: resurrection and redescription of Ahaetulla flavescens (Wall, 1910) (Reptilia: Serpentes: Colubridae)

Fig. 3. Dryophis prasinus var. flavescens Wall, 1910, lectotype (NHMUK 1908.6.23.58). Entire profile, dorsal and ventral views. Photo: ©The Trustees of the Natural History Museum, London.

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Structure of single-walled carbon nanotubes

Structure of single-walled carbon nanotubes Junjie Chen Department of Energy and Power Engineering, School of Mechanical and Power Engineering, Henan Polytechnic University, 2000 Century Avenue, Jiaozuo, Henan, 454000, P.R. China Contributor: Junjie Chen, ORCID: 0000-0002-5022-6863, E-mail address: koncjj@gmail.com   Carbon nanotubes take on many different forms but generally fall into two groups. The first group is multi-walled carbon nanotubes and the second group is single-walled carbon nanotubes. A multi-walled carbon nanotube is basically a nested formation of multi-axial layered carbon pipes with caps at either end of the cylinder structure and can be created with various chemical reactions but are commonly fabricated using a form of carbon arc discharge in the proper environment. A single-walled carbon nanotube is essentially a rolled-up graphite sheet that forms a very small thin cylinder with no seam. The fabrication of a single-walled carbon nanotube is similar to a multi-walled carbon nanotube with the addition of a metallic catalyst. The length and diameter of a single-walled carbon nanotube is dependent on the type of metallic catalyst used and the environmental conditions employed during fabrication. Single-walled carbon nanotubes are of interest as they could play the same role in circuits as silicon does today. The advantage of single-walled carbon nanotubes is that they form naturally much smaller than most silicon transistors. This drastic reduction is size could result in a dramatic increase in the processing speed of electronics due to the reduced distances signals would have to travel. Single-walled carbon nanotubes have been obtained in early fabrication techniques using a carbon arc chamber similar to that used for fullerene production. An anode consisting of a graphite carbon rod and a cathode consisting of a rod with a piece of iron placed in a small dimple therein are placed in the chamber that is filled with methane and argon. The single-walled carbon nanotubes were found in soot-like deposits formed during the carbon arc process. A slightly different single-walled carbon nanotube was obtained using cobalt instead of iron and helium instead of methane and argon. Known methods of fabrication of single-walled carbon nanotubes result in a combination of semiconductors and conductors. Additionally, known methods of fabrication of single-walled carbon nanotubes result in very impure carbon nanotubes in that a low percentage of the resulting material constitutes single-walled carbon nanotubes. The use of known fabrication methods requires extensive purification processes afterward to remove the non-single-walled carbon nanotube structure. As the impurities are often larger than or similar in size to the single-walled carbon nanotubes, the use of filtering in the purification process proves difficult. Furthermore, known fabrication methods are inefficient, in that only one or two grams of carbon nanotubes are likely to be produced. These early fabrication techniques produced impure carbon nanotubes and only in small numbers. The catalytic materials used in single-walled carbon nanotube fabrication prevent the large scale fairly pure production of these structures. To date, other fabrication techniques have indicated little if any promise of being scaled into mass production of single-walled carbon nanotubes in either pure or impure form. In addition, all known production methods are labor and chemical intensive, thus making them very costly. The cylindrical sidewalls can be produced from different rolling directions to make single-walled carbon nanotube with distinct structures and properties. Due to cylindrical symmetry, there are only a handful of methods that are effective in making seamless cylinders, and they are characterized by the chiral vectors with integer indices. To establish the chiral vector, two atoms in the graphene sheet are selected, with one serving as the origin of the vector pointing toward the other atom. The graphene sheet is then rolled in a way that allows the two atoms to coincide. These structural variations result in differences in electrical conductivity and mechanical strength.

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Structure of single-walled carbon nanotube reinforced polymer matrix composites

Structure of single-walled carbon nanotube reinforced polymer matrix composites Junjie Chen Department of Energy and Power Engineering, School of Mechanical and Power Engineering, Henan Polytechnic University, 2000 Century Avenue, Jiaozuo, Henan, 454000, P.R. China Contributor: Junjie Chen, ORCID: 0000-0002-5022-6863, E-mail address: koncjj@gmail.com   A composite material, also called a composite, is a solid material that results when two or more different substances, each with its own characteristics, are combined to create a new substance whose properties are superior to those of the original components in a specific application. The term composite more specifically refers to a structural material within which a fibrous material is embedded. The remarkable properties of composites are achieved by embedding fibers of one substance in a host matrix of another. In materials science, a polymer matrix composite is a composite material composed of a variety of short or continuous fibers bound together by a matrix of organic polymers. Polymer matrix composites are designed to transfer loads between fibers of a matrix. Some of the advantages with polymer matrix composites include their light weight, high resistance to abrasion and corrosion, and high stiffness and strength along the direction of their reinforcements. The function of the matrix in polymer matrix composites is to bond the fibers together and transfer loads between them. Polymer matrix composites matrices are typically either thermosets or thermoplastics. Thermosets are by far the predominant type in use today. Thermosets are subdivided into several resin systems including epoxies, phenolics, polyurethanes, and polyimides. Of these, epoxy systems currently dominate the advanced composite industry. Unlike fiber-reinforced polymer matrix composites, nanomaterials reinforced polymer matrix composites are able to achieve significant improvements in mechanical properties at much lower loadings. Carbon nanotubes in particular have been intensely studied due to their exceptional intrinsic mechanical properties and low densities. In particular carbon nanotubes have some of the highest measured tensile stiffnesses and strengths of any material due to the strong covalent bonds between carbon atoms. However, in order to take advantage of the exceptional mechanical properties of the nanotubes, the load transfer between the nanotubes and matrix must be very large. Like in fiber-reinforced composites, the size dispersion of the carbon nanotubes significantly affects the final properties of the composite. Long carbon nanotubes lead to an increase in tensile stiffness and strength due to the large-distance stress transfer and crack propagation prevention. On the other hand, short carbon nanotubes do not lead to any enhancement of properties without any interfacial adhesion. However once modified, short carbon nanotubes are able to further improve the stiffness of the composite, however there is still very little crack propagation countering. In general, long and high aspect ratio carbon nanotubes lead to greater enhancement of mechanical properties, but are more difficult to process. Aside from size, the interface between the carbon nanotubes and the polymer matrix is of exceptional importance. In order to achieve better load transfer, a number of different methods have been used to better bond the carbon nanotubes to the matrix by functionalizing the surface of the carbon nanotube with various polymers. These methods can be divided into non-covalent and covalent strategies. Non-covalent carbon nanotube modification involves the adsorption or wrapping of polymers to the carbon nanotube surface, usually via van der Waal's or π-stacking interactions. In contrast, covalent functionalization involves direct bonding onto the carbon nanotube. This can be achieved in a number of ways, such as oxidizing the surface of the carbon nanotube and reacting with the oxygenated site, or using a free radical to directly react with the carbon nanotube lattice. Covalent functionalization can be used to directly attach the polymer to the carbon nanotube, or to add an initiator molecule which can then be used for further reactions.

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Thermodynamics of single-walled carbon nanotubes

Thermodynamics of single-walled carbon nanotubes Junjie Chen Department of Energy and Power Engineering, School of Mechanical and Power Engineering, Henan Polytechnic University, 2000 Century Avenue, Jiaozuo, Henan, 454000, P.R. China Contributor: Junjie Chen, ORCID: 0000-0002-5022-6863, E-mail address: koncjj@gmail.com   A system's condition at any given time is called its thermodynamic state. For a gas in a cylinder with a movable piston, the state of the system is identified by the temperature, pressure, and volume of the gas. These properties are characteristic parameters that have definite values at each state and are independent of the way in which the system arrived at that state. In other words, any change in value of a property depends only on the initial and final states of the system, not on the path followed by the system from one state to another. Such properties are called state functions. In contrast, the work done as the piston moves and the gas expands and the heat the gas absorbs from its surroundings depend on the detailed way in which the expansion occurs. The behavior of a complex thermodynamic system can be understood by first applying the principles of states and properties to its component parts, in this case, water, water vapor, and the various gases making up the atmosphere. By isolating samples of material whose states and properties can be controlled and manipulated, properties and their interrelations can be studied as the system changes from state to state. The concept of temperature is fundamental to any discussion of thermodynamics, but its precise definition is not a simple matter. It is necessary to have an objective way of measuring temperature. In general, when two objects are brought into thermal contact, heat will flow between them until they come into equilibrium with each other. When the flow of heat stops, they are said to be at the same temperature. The zeroth law of thermodynamics formalizes this by asserting that if an object A is in simultaneous thermal equilibrium with two other objects B and C, then B and C will be in thermal equilibrium with each other if brought into thermal contact. Object A can then play the role of a thermometer through some change in its physical properties with temperature, such as its volume or its electrical resistance. Energy has a precise meaning in physics that does not always correspond to everyday language, and yet a precise definition is somewhat elusive. The word is derived from the Greek word ergon, meaning work, but the term work itself acquired a technical meaning with the advent of Newtonian mechanics. As the science of physics expanded to cover an ever-wider range of phenomena, it became necessary to include additional forms of energy in order to keep the total amount of energy constant for all closed systems or to account for changes in total energy for open systems. Thermodynamics encompasses all of these forms of energy, with the further addition of heat to the list of different kinds of energy. However, heat is fundamentally different from the others in that the conversion of work or other forms of energy into heat is not completely reversible, even in principle. Although classical thermodynamics deals exclusively with the macroscopic properties of materials, such as temperature, pressure, and volume, thermal energy from the addition of heat can be understood at the microscopic level as an increase in the kinetic energy of motion of the molecules making up a substance. For example, gas molecules have translational kinetic energy that is proportional to the temperature of the gas: the molecules can rotate about their center of mass, and the constituent atoms can vibrate with respect to each other. Additionally, chemical energy is stored in the bonds holding the molecules together, and weaker long-range interactions between the molecules involve yet more energy. The sum total of all these forms of energy constitutes the total internal energy of the substance in a given thermodynamic state. The total energy of a system includes its internal energy plus any other forms of energy, such as kinetic energy due to motion of the system as a whole and gravitational potential energy due to its elevation.

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Thermodynamics of double-walled carbon nanotubes

Thermodynamics of double-walled carbon nanotubes Junjie Chen Department of Energy and Power Engineering, School of Mechanical and Power Engineering, Henan Polytechnic University, 2000 Century Avenue, Jiaozuo, Henan, 454000, P.R. China Contributor: Junjie Chen, ORCID: 0000-0002-5022-6863, E-mail address: koncjj@gmail.com   Thermodynamics deals with the transfer of energy from one place to another and from one form to another. The most important laws of thermodynamics are stated herein. The zeroth law of thermodynamics. When two systems are each in thermal equilibrium with a third system, the first two systems are in thermal equilibrium with each other. This property makes it meaningful to use thermometers as the third system and to define a temperature scale. The first law of thermodynamics. The change in a system's internal energy is equal to the difference between heat added to the system from its surroundings and work done by the system on its surroundings. The second law of thermodynamics. Heat does not flow spontaneously from a colder region to a hotter region, or, equivalently, heat at a given temperature cannot be converted entirely into work. Consequently, the entropy of a closed system, or heat energy per unit temperature, increases over time toward some maximum value. Thus, all closed systems tend toward an equilibrium state in which entropy is at a maximum and no energy is available to do useful work. The third law of thermodynamics. The entropy of a perfect crystal of an element in its most stable form tends to zero as the temperature approaches absolute zero. This allows an absolute scale for entropy to be established that, from a statistical point of view, determines the degree of randomness or disorder in a system. The laws of thermodynamics are deceptively simple to state, but they are far-reaching in their consequences. The first law is put into action by considering the flow of energy across the boundary separating a system from its surroundings. Consider the classic example of a gas enclosed in a cylinder with a movable piston. The walls of the cylinder act as the boundary separating the gas inside from the world outside, and the movable piston provides a mechanism for the gas to do work by expanding against the force holding the piston in place. If the gas does work as it expands, and absorbs heat from its surroundings through the walls of the cylinder, then this corresponds to a net flow of energy across the boundary to the surroundings. In order to conserve the total energy, there must be a counterbalancing change in the internal energy of the gas. From a formal mathematical point of view, the incremental change in the internal energy is an exact differential, while the corresponding incremental changes in heat and work are not, because the definite integrals of these quantities are path-dependent. These concepts can be used to great advantage in a precise mathematical formulation of thermodynamics. The science of thermodynamics provides a rich variety of formulas and techniques that allow the maximum possible amount of information to be extracted from a limited number of laboratory measurements of the properties of materials. However, as the thermodynamic state of a system depends on several variables, such as temperature, pressure, and volume, in practice it is necessary first to decide how many of these are independent and then to specify what variables are allowed to change while others are held constant. For this reason, the mathematical language of partial differential equations is indispensable to the further elucidation of the subject of thermodynamics. Of especially critical importance in the application of thermodynamics are the amounts of work required to make substances expand or contract and the amounts of heat required to change the temperature of substances. The first is determined by the equation of state of the substance and the second by its heat capacity. Once these physical properties have been fully characterized, they can be used to calculate other thermodynamic properties, such as the free energy of the substance under various conditions of temperature and pressure.

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