Are single crystals isotropic or anisotropic?
Most single crystals show anisotropy in certain properties, such as optical and mechanical properties. An amorphous substance, such as window glass, tends to be isotropic . This difference may make it possible to distinguish between a glass and a crystal.
What is the difference between single crystal and polycrystalline?
Single crystals have infinite periodicity, polycrystals have local periodicity, and amorphous solids (and liquids) have no long-range order. A polycrystalline solid or polycrystal is comprised of many individual grains or crystallites.
Why are crystals anisotropic?
Crystalline solids are anisotropic in nature, that is, some of their physical properties like electrical resistance or refractive index show different values when measured along different directions in the same crystals. This arises from different arrangement of particles in different directions.
What is isotropic and anisotropic material?
Isotropic refers to the properties of a material which is independent of the direction whereas anisotropic is direction-dependent. Some examples of isotropic materials are cubic symmetry crystals, glass, etc. Some examples of anisotropic materials are composite materials, wood, etc.
What are anisotropic materials?
Anisotropic Materials. Anisotropic materials are materials whose properties are directionally dependent. Unlike. isotropic materials that have material properties identical in all directions, anisotropic material’s properties such as Young’s Modulus, change with direction along the object.
Is Bone anisotropic?
Bones, from a macroscopic point of view, can be classified as non-homogeneous, porous and anisotropic tissue, (Doblaré et al. 2004).
Is plastic anisotropic?
Plastic anisotropy is the result of the distortion of the yield surface shape due to the material microstructural state. Regardless of the shape of the yield surface, strain hardening can be isotropic or anisotropic.
Why bone is strongest along long axis?
A long bone acts strongest when stressed by forces acting along the long axis of the bone, as occurs during compression. Bone suffers when handling forces applied transversely across its surface. These bones, and all bone in general, function strongest in compression and weakest in shear.
Why is bone viscoelastic?
The viscoelasticity of bone can therefore arise from the void collapse and deossification of cancellous bone and the natural viscoelastic response of collagen as a polymer.
What is viscoelastic behavior?
Viscoelastic behaviour is a combination of elastic and viscous behaviour where the applied stress results in an instantaneous elastic strain followed by a viscous, time-dependent strain.
What is viscoelastic substance?
5.1. 4 Viscoelastic Material. A viscoelastic material possesses both viscous and elastic characteristics under loading. A vehicular shock absorber, made of a spring and a damper, is a typical structural component that behaves in a viscoelastic manner.
What is Viscoat used for?
The main reason for using OVDs in cataract surgery is to prevent damage of the corneal endothelium. Dispersive OVDs, such as Viscoat, are considered to protect the endothelium better than cohesive OVDs, because of their lower specific surface properties [2].
What is Healon used for?
The HEALON® PRO OVD is indicated for use as a surgical aid in cataract extraction (intra- and extracapsular), IOL implantation, corneal transplant, glaucoma filtration and retinal attachment surgery.
What is Provisc?
Provisc (1% sodium hyaluronate) is an ophthalmic surgical aid used in the anterior segment during cataract extraction and intraocular lens (IOL) implantation.
Why are OVDs used during cataract surgery?
OVDs are routinely used in cataract surgery to protect delicate ocular structures, compartmentalize within the eye, pressurize the anterior chamber, and provide a faster and safer surgery with better visual recovery for our patients.
What is Ocucoat?
OCUCOAT (hydroxypropylmethylcellulose) is a sterile, isotonic, nonpyrogenic viscoelastic solution of highly purified, noninflammatory, 2% hydroxypropylmethylcellulose with a high molecular weight greater than 80,000 daltons. OCUCOAT (hydroxypropylmethylcellulose) is supplied in 1 mL syringes.
What is Healon GV?
HEALON® GV OVD HEALON GV® OVDs offer high viscosity for deep anterior chamber creation and maximum space for maneuverability with minimal damage to the cornea or other delicate ocular tissues.
How many OVDs are there as per RBI?
six OVDs
What is viscoelastic in cataract surgery?
Viscoelastics, also referred to as ophthalmic viscosurgical devices, or OVDs, are viscous substances that allow us to make phacoemulsification easier and safer. Once the first incision is made into the eye, it has a tendency to collapse as the aqueous leaks out.
What is the function of Capsulorhexis?
Capsulorhexis or capsulorrhexis, also known as continuous curvilinear capsulorhexis (CCC), is a technique pioneered by Howard Gimbel used to remove the capsule of the lensfrom the eye during cataract surgery by shear and stretch forces.
How do you perform Capsulorhexis?
To initiate the capsulorhexis, use a bent needle cystotome to create a radial incision from the center of the lens to the desired radius of the capsulorhexis, then pull down to create a flap. Creating a flap that is too short will result in an opening that is too small.
What is the meaning of capsulotomy?
Capsulotomy (BrE /kæpsjuː’lɒtəmi/, AmE /kæpsuː’lɑːtəmi/) is a type of eye surgery in which an incision is made into the capsule of the crystalline lens of the eye. In modern cataract operations, the lens capsule is usually not removed.
What does phacoemulsification mean?
Phacoemulsification is a modern cataract surgery method in which the eye’s internal lens is emulsified with an ultrasonic handpiece and aspirated from the eye. Aspirated fluids are replaced with irrigation of balanced salt solution to maintain the anterior chamber.
Is phacoemulsification safe?
Conclusions: Both the phacoemulsification and the small-incision techniques are safe and effective for visual rehabilitation of cataract patients, although phacoemulsification gives better uncorrected visual acuity in a larger proportion of patients at 6 weeks.
Which is better laser or traditional cataract surgery?
Compared to traditional cataract surgery, the laser-assisted approach offers a myriad of advantages. First, the use of a computer-guided laser means the surgical incision is up to 10 times more accurate than a corneal incision done by hand. Recovery is also smoother after bladeless laser-assisted cataract surgery.
Which is better phaco or sics?
CONCLUSION. Manual SICS and phacoemulsification do not differ significantly in complication rates and final CDVA outcomes. However, manual SICS is significantly faster. It may be the preferred technique in settings where surgical volume is high and access to phacoemulsification is limited, such as in eye camps.
How do you do phacoemulsification?
How Is Phacoemulsification Performed? During phacoemulsification, a surgeon makes a small incision at the edge of the cornea and then creates an opening in the membrane that surrounds the lens. A small ultrasonic probe is then inserted, breaking up the cloudy lens into tiny fragments.
When did cataract surgery become routine?
The first true cataract extraction was performed in 1747, in Paris, by the French surgeon Jacques Daviel. His procedure was more effective than couching, with an overall success rate of 50%.