Argon Laser Light Research Articles

The Influence of Nystatin and Argon Laser Combination on Candida Albicans and Actinomycetes Isolated from Oral Cavity of Children

The present study has been undertaken to illustrate the effect of argon laser and nystatin on isolated candida albican andActinomycetes from oral cavity of children. Out of 20 samples, positive cultures were 26 bacterial samples and 12 fungussamples, the isolated bacteria included Staphylococcus aureus ,klebseilla pneumonias ,and streptococcus viridans .The isolated fungi included candida albican and Actinomycetes. The present study shows that determination of minimal inhibitoryconcentrations of nystatin ranged from 1-12 i.u./ml in sabroud agar plates were prepared and cultured with tested fungi ,incubatedat 25 oC for 24-48 hrs.The candida albican and Actinomycetes fungi exposed to argon ion (Ar+) laser after focal with a lens of(15) cm after focal point for periods of time(1,1.5,2,4,6,8,10,12,14,16)min, and shows the effect of combination between nystatin and laser light.The result showed that the minimal inhibitory concentrations of nystatin for candida albican were 1-12 i.u./ml but the minimal inhibitory concentrations of nystatin for Actinomycetes were 3-12 i.u./ml .Also it is found that candida albican completely killed after exposure to argon laser for 12-16 minutes. While Actinomycetes completely killed after exposure to argon laser for 10-16 minutes.The combination between laser and nystatin were more effective,all candida albican isolated from oral cavity were killedafter exposure to (argon laser light , nystatin combination) for 10 minutes / 7 i.u./ml, while all Actinomycetes killed after exposureto (argon laser light ,nystatin combination) for 6 minutes/5 i.u./ml .The widly uses of laser in oral and dental treatment encourages to further investigations . Recent advances has shown the save and destructive results by using laser open the hopes to introduce laserstrongly in treatment of oral and dental diseases

In vitro study - Comparative evaluation of bond strengths of stainless steel brackets and ceramic brackets after curing with the argon laser and the conventional visible light

Aim:The purpose of this study was to compare the bond strengths of stainless steel brackets and ceramic brackets after treated with conventional visible light and argon laser.Methodology:Extracted 80 human premolar teeth were collected and stored in distilled water. They are classified into four groups. All teeth were placed in acrylic block where long axis of the tooth should be perpendicular to the mold's bottom. Teeth were subjected to ×10 magnification after debonding.Results:There is no statistically significant difference was found between the shear bond strength of argon laser and conventional visible light for stainless steel and ceramic bracket. Ceramic brackets had significantly increased bond strength than stainless steel brackets.Conclusion:Argon laser can be used for bonding orthodontic brackets using a visible light-cure orthodontic adhesive system, and ceramic brackets had significantly increased bond strength than stainless steel.

Progress Toward Optical Biopsy: Bringing the Microscope to the Patient

The investigation of many lung diseases currently requires bronchoscopic or surgical histopathological tissue biopsy. This creates risks for patients and entails processing costs and delays in diagnosis. However, several mainly probe-based biophotonic techniques that can image solitary lesions and diffuse lung diseases are fuelling a paradigm shift toward real-time in vivo diagnosis. Optical coherence tomography (OCT) uses near-infrared light in a process analogous to ultrasonography to image the mucosal and submucosal tissue boundaries of the bronchial tree. With 15-μm resolution, early work suggests it can differentiate between neoplasia, carcinoma in situ, dysplasia, and metaplasia based around epithelial thickness and breaches in the basement membrane. Probe-based confocal laser endomicroscopy (pCLE) has superior resolution but less penetration than OCT and employs blue argon laser light to fluoresce the endogenous elastin of (1) the acinar scaffold of the peripheral lung and (2) the basement membrane lying under bronchial mucosa. Initial studies suggest that the regular fibre arrangement of the basement membrane is altered in the presence of overlying malignant epithelium. pCLE produces detailed representations of the alveolar septal walls, microvessels, and some inflammatory cells. A third device, the endocytoscope, is a contact microscope requiring contrast agent to provide subcellular resolution of bronchial mucosa. Further development of these "optical biopsy" techniques and evaluation of diagnostic sensitivity and specificity of the acquired images are needed before they can be considered effective methods for eliminating the need for, and thus risks of, pinch biopsy to enable real-time diagnosis to streamline management.

Hybrid-polymer nanostructures forming an anti-reflection film using two-beam interference and ultraviolet nanoimprint lithography

This study presents a new process to fabricate the two-dimensional periodic nanostructures with the specific material of inorganic–organic hybrid polymers (ORMOCER). In this study, the photoresist (PR) originated nanostructures can be fabricated with a two-beam interference method by use of 351 nm-wavelength Argon ion laser light. The replicated mold is performed by Ni electroless plating that Ni mold can be used by ultraviolet nanoimprint lithography (UV-NIL) process imprinting into the hybrid-polymer surface. The hybrid-polymer material is coating on the flexible polyethylene terephthalate (PET). Here, a self-assembled monolayer of fluoroalkyl silane (FAS-SAM) can be effective by means of atmospheric-pressure plasma (AP) chemical vapor modification of Ni mold surface for the duplicated ORMOCER/PET nanostructure film in UV-NIL process.

Bidirectional Photoresponse of Surface Pretreated Azobenzene Liquid Crystal Polymer Networks

We report on the photodriven, polarization-controlled response of UV-pretreated azobenzene-based liquid crystal polymer networks (azo- LCN) of polydomain orientation to higher wavelength CW argon-ion laser light (Ar(+)) of 457-514 nm. The significant absorbance of the azo-LCN cantilever in the UV is used to form an approximately 1 microm thick cis-isomer rich skin. Subsequent exposure to the Ar(+) laser drives a bidirectional bending process that is the result of two distinguishable photochemical processes. First, 457-514 nm laser light (regardless of polarization state) drives cis-trans photoisomerization of the UV-pretreated surface, restoring the order of the azobenzene liquid crystalline moieties. Mechanically, the cis-trans process results in an expansion on the exposed surface that forces the cantilever to undergo a rapid bend away from the laser source. Once a sufficient number of trans-azobenzene moieties are regenerated, continued Ar(+) illumination promotes both the trans-cis and cis-trans processes enabling trans-cis-trans reorientation. In this particular system and conditions, trans-cis-trans reorientation enables polarization controlled mechanical bending of different angles towards the Ar(+) source. Photomechanical responses of UV-pretreated azo-LCN demonstrate the viability of photogenerated effects in UV-rich environments such as space.

Integrin-linked Kinase Regulates N-WASp-mediated Actin Polymerization and Tension Development in Tracheal Smooth Muscle

The contractile stimulation of smooth muscle tissues stimulates the recruitment of proteins to membrane adhesion complexes and the initiation of actin polymerization. We hypothesized that integrin-linked kinase (ILK), a beta-integrin-binding scaffolding protein and serine/threonine kinase, and its binding proteins, PINCH, and alpha-parvin may be recruited to membrane adhesion sites during contractile stimulation of tracheal smooth muscle to mediate cytoskeletal processes required for tension development. Immunoprecipitation analysis indicted that ILK, PINCH, and alpha-parvin form a stable cytosolic complex and that the ILK.PINCH.alpha-parvin complex is recruited to integrin adhesion complexes in response to acetylcholine (ACh) stimulation where it associates with paxillin and vinculin. Green fluorescent protein (GFP)-ILK and GFP-PINCH were expressed in tracheal muscle tissues and both endogenous and recombinant ILK and PINCH were recruited to the membrane in response to ACh stimulation. The N-terminal LIM1 domain of PINCH binds to ILK and is required for the targeting of the ILK-PINCH complex to focal adhesion sites in fibroblasts during cell adhesion. We expressed the GFP-PINCH LIM1-2 fragment, consisting only of LIM1-2 domains, in tracheal smooth muscle tissues to competitively inhibit the interaction of ILK with PINCH. The PINCH LIM1-2 fragment inhibited the recruitment of endogenous ILK and PINCH to integrin adhesion sites and prevented their association of ILK with beta-integrins, paxillin, and vinculin. The PINCH LIM1-2 fragment also inhibited tension development, actin polymerization, and activation of the actin nucleation initiator, N-WASp. We conclude that the recruitment of the ILK.PINCH.alpha-parvin complex to membrane adhesion complexes is required to initiate cytoskeletal processes required for tension development in smooth muscle.

Whole-Wafer Mapping of Dislocations in 4H-SiC Epitaxy

A non-destructive technique to image the dislocations and other extended defects in SiC epitaxial layers has been developed. Basal plane dislocations (BPDs) and threading dislocations (TDs) are imaged. Photoluminescence from the dislocations is excited with the 364 and/or 351 nm lines of an argon ion laser and near-infrared light is collected. A computer controlled probe station takes multiple images and the mm-sized images are stitched together to form whole-wafer maps. The technique is applied to a set of four n+ wafers from the same boule with 50 um n- epitaxial layers. The epitaxy was grown with Cree’s low-BPD process. BPDs form as either single, isolated dislocations or as clusters encircling micropipes. The concentration of TDs is on the order 104/cm2 and the local concentration varies more than an order of magnitude. The advantages of mapping dislocations by UV-PL imaging compared to other techniques are discussed.

The luminescence of Pr3+ ions doped in Y4Al2O9 by sol–gel synthesis

Abstract The Pr3+-doped Y4Al2O9 powders were synthesized by sol–gel method. Powder X-ray diffraction and SEM techniques were used to check for Y4Al2O9 powders. The Li+ co-doping with Pr3+ has an influence on the sintering temperature and morphology of the Y4Al2O9 powders produced from the gel. The emission spectra under different excitations, e.g., the 488 nm line of an argon-ion laser, X-ray and UV light, were investigated. The luminescence intensity of Y4Al2O9:Pr3+ could be increased with Li+ co-doping. Luminescence properties of Pr3+ ions in the two samples have some difference. In the Y4Al2O9:Pr3+, the emission at 490 nm from 3P0 is dominant, while, the Y4Al2O9:(Pr3+ + Li+) system was characterized by a red emission at 607 and 610 nm corresponding to the 1D2 → 3H4 inner transition of Pr3+ ions; and these two emissions show different excitation band from the 4f5d state.

Engineered Monomeric Human Histidine Triad Nucleotide-binding Protein 1 Hydrolyzes Fluorogenic Acyl-adenylate and Lysyl-tRNA Synthetase-generated Lysyl-adenylate

Hint1 is a homodimeric protein and member of the ubiquitous HIT superfamily. Hint1 catalyzes the hydrolysis of purine phosphoramidates and lysyl-adenylate generated by lysyl-tRNA synthetase (LysRS). To determine the importance of homodimerization on the biological and catalytic activity of Hint1, the dimer interface of human Hint1 (hHint1) was destabilized by replacement of Val(97) of hHint1 with Asp, Glu, or Arg. The mutants were shown to exist as monomers in solution by a combination of size exclusion chromatograph, static light scattering, and chemically induced dimerization studies. Circular dichroism studies revealed little difference between the stability of the V97D, V97E, and wild-type hHint1. Relative to wild-type and the V97E mutant, however, significant perturbation of the V97D mutant structure was observed. hHint1 was shown to prefer 3-indolepropionic acyl-adenylate (AIPA) over tryptamine adenosine phosphoramidate monoester (TpAd). Wild-type hHint1 was found to be 277- and 1000-fold more efficient (k(cat)/K(m) values) than the V97E and V97D mutants, respectively. Adenylation of wild-type, V97D, and V97E hHint1 by human LysRS was shown to correlate with the mutant k(cat)/K(m) values using 3-indolepropionic acyl-adenylate as a substrate, but not tryptamine adenosine phosphoramidate monoester. Significant perturbations of the active site residues were not detected by molecular dynamics simulations of the hHint1s. Taken together, these results demonstrate that for hHint1; 1) the efficiency (k(cat)/K(m)) of acylated AMP hydrolysis, but not maximal catalytic turnover (k(cat)), is dependent on homodimerization and 2) the hydrolysis of lysyl-AMP generated by LysRS is not dependent on homodimerization if the monomer structure is similar to the wild-type structure.

Increases in intrapulpal temperature during polymerization of composite resin

The polymerization of dental composite resins can generate increases in intrapulpal temperature that may damage the pulp. The development of new polymerization devices such as the argon laser makes the assessment of these temperatures important. This study compared increases in temperature generated by argon laser and halogen light when polymerizing a bonding system and a composite resin, and also sought to determine whether both types of polymerization lights generate temperature increases below the safe limit of 5.5 degrees C. Thermocouples linked to a temperature reading system were positioned in the pulp chamber of 10 extracted bovine incisors. Class V cavities were prepared, etched, and filled with a 1-bottle bonding system (Single Bond) and composite resin (Z-100). The test groups were as follows (n = 5 for all groups): halogen light for bonding system (HB); halogen light for composite resin (HC); argon laser for bonding system (LB), and argon laser for composite resin (LC). The polymerization parameters were halogen light operated at 600 mW/cm2 for 40 seconds, which served as control, and argon laser operated at 200 mW for 10 seconds. Data were analyzed by a 2-way (light versus material) analysis of variance (ANOVA) (alpha = .05). The average temperature increases were 2.35 degrees C (HB), 2.69 degrees C (HC), 1.25 degrees C (LB), and 1.5 degrees C (LC). Significant differences between halogen light and argon laser (P = .002), but not between composite and bonding system, were demonstrated. The argon laser produced significantly lower increases in pulpal temperature than the halogen light, independent of the thickness of the polymerized material.

Study of sensitometric and holographic properties of photoresist media based on carbazole-containing polymers sensitized with triiodomethane and pyran photochromic materials

Sensitometric and holographic properties of photoresist layers made from carbazolylalkyl methacrylate copolymers and polyepoxypropylcarbazole sensitized with triiodomethane and, additionally, spiropyran photochromic compounds were studied. It was found that the introduction of photochromic 6′-bromo-8′-nitro-1,3,3-trimethylindolylspirobenzopyran (8–12%) into photoresist layers increased their photographic sensitivity by a factor of 2.5–3 up to the values of 10−3–10−4 J cm−2 and shifted their spectral sensitivity to the blue-green region. The feasibility of recording quality holograms in the photoresist layers using coherent He-Cd laser light (λ = 420 nm), as well as argon laser light (λ = 490 nm), was shown. Diffraction gratings with an efficiency of 15–20% and a resolution of 2000 mm−1 were obtained.

Curcumin Selectively Induces Apoptosis in Deregulated Cyclin D1-expressed Cells at G2 Phase of Cell Cycle in a p53-dependent Manner

Curcumin (diferuloylmethane) is known to induce apoptosis in tumor cells. In asynchronous cultures, with time-lapse video-micrography in combination with quantitative fluorescence microscopy, we have demonstrated that curcumin induces apoptosis at G(2) phase of cell cycle in deregulated cyclin D1-expressed mammary epithelial carcinoma cells, leaving its normal counterpart unaffected. In our search toward delineating the molecular mechanisms behind such differential activities of curcumin, we found that it selectively increases p53 expression at G(2) phase of carcinoma cells and releases cytochrome c from mitochondria, which is an essential requirement for apoptosis. Further experiments using p53-null as well as dominant-negative and wild-type p53-transfected cells have established that curcumin induces apoptosis in carcinoma cells via a p53-dependent pathway. On the other hand, curcumin reversibly inhibits normal mammary epithelial cell cycle progression by down-regulating cyclin D1 expression and blocking its association with Cdk4/Cdk6 as well as by inhibiting phosphorylation and inactivation of retinoblastoma protein. In addition, curcumin significantly up-regulates cell cycle inhibitory protein (p21Waf-1) in normal cells and arrests them in G(0) phase of cell cycle. Therefore, these cells escape from curcumin-induced apoptosis at G(2) phase. Interestingly, these processes remain unaffected by curcumin in carcinoma cells where cyclin D1 expression is high. Similarly, in ectopically overexpressed system, curcumin cannot down-regulate cyclin D1 and thus block cell cycle progression. Hence, these cells progress into G(2) phase and undergo apoptosis. These observations together suggest that curcumin may have a possible therapeutic potential in breast cancer patients.

Penetration depth of light for argon laser curing of dental composites

Abstract Polymerization of dental restorative materials as light-activated tooth-colored composites can be done using argon laser light of 488 nm. This study calculates the effective penetration depth of light at 490 nm in different composites and shades in order to gain information for a comparison of the curing properties of the composite resins after argon laser polymerization. Penetration depth was calculated by diffusion theory on the basis of the optical parameters of the composites and shades, as there are the absorption coefficient μ a , the scattering coefficient μ s , and the anisotropy factor g. To determine these optical parameters, a method which includes sample preparation and measurements of transmission and reflectance in an integrating sphere spectrometer followed by inverse Monte Carlo simulations has been used. The calculated penetration depths differ between the investigated composite systems and between the shades. The results are suitable for a relative comparison of different composites and shades. They allow conclusions to be drawn about the expected depth of cure, insofar as a composite with a lower penetration depth of the used curing wavelength will also show a lower depth of cure with a lower degree of conversion compared to a composite with a higher penetration depth of the same curing wavelength.

Photodynamic Effect of Modulated and Continuous LASER Radiation on Cancerous Cells Cultivated In Vitro

Photodynamic therapy (PDT) is a cancer therapy that uses nonionizing photons and a photosensitizer to treat solid tumors and surface malignancies. Experiments with cells in vitro have been useful in order to investigate cellular effects due to PDT. In this work, we study the photodynamic effect of modulated and continuous laser radiation on cancerous cells cultivated in vitro. Three experiments were performed for this study. For the first one, HeLa cells were exposed to δ-Aminolevulinic acid (ALA) at concentrations of 0, 10, 20, 40, 80 and 160 µg of ALA/ml of Dulbecco's modified Eagle's medium (DMEM) and were irradiated at total light dose of 80 J/cm2 by using continuous and modulated argon laser light. In the case of modulated radiation, at 1000 Hz, we observed more cellular death (20%) than those produced by continuous light (0%) when these cells were exposed at 20 µg of ALA/ml of DMEM. For other ALA doses cellular deaths were similar in both irradiation types. The death percentage in cancerous cell, after application of PDT with continuous and modulated irradiation, was determined by means of the neutral-red spectrophotometric assay. In the second experiment HeLa cells were exposed only at 20 µg of ALA/ml of DMEM and irradiated with argon laser at total light dose of 80 J/cm2 but using different light modulation frequencies: 100, 160, 600, 1250, 1500, 1850 Hz. Finally in the third experiment, where the HeLa cells were exposed in the same conditions of second experiment, the modulation frequencies used to irradiate the cell were: 10, 20, 40, 80 Hz. It was observed that light modulation frequency at 40 Hz produces maximum cellular death (36%). These results showed that modulated light used in PDT, for low ALA doses in HeLa cells, is more efficient than continuous light irradiation. Modulated irradiation in PDT could reduce the quantity of required ALA, and in consequence to reduce possible collateral damage, for application of this therapy.

Root apex sealing with different filling materials photopolymerized with fiber optic?delivered argon laser light

The present study evaluates the seal quality in the apex delta of uniradicular teeth filled with light-cured materials (calcium hydroxide, glass ionomer, and Flow-Fill Magic composite). A total of 45 roots prepared by the endo PTC/Dakin technique were used. All sample restorations were light-cured with 488-nm argon laser light. A 200-microm optical fiber introduced into the root canal delivered 100 mW of light power to the filler material. The fiber tip was positioned 5 mm away from the apex. Light was applied for 20 s. After curing, the samples were immersed in a methylene blue solution for 24 h. Then the samples were cut longitudinally and analyzed under a stereoscopic microscope for dye infiltration. For the sake of comparison, an additional group of ten samples submitted to conventional treatment with EndoREZ root canal sealer was also analyzed. The samples sealed with calcium hydroxide or with the glass ionomer presented less dye infiltration, as compared to those sealed with the Flow-Fill Magic composite. All products activated by fiber optic-delivered light showed superior sealing quality when compared with the self-activated EndoREZ sealer.

Contribution of Absorptive and Refractive Gratings to Mixed Holograms Using Xanthene-Dye-Doped Films

The contribution of absorptive and refractive gratings to a mixed hologram is investigated by means of two-wave coupling technique by moving a hologram. Polyvinyl alcohol films doped with xanthene-dyes such as erythrosin B,eosin Y, uranin and fluorescein which absorb an argon-ion laser light of 488 nm and 515 nm are used as hologram recording materials in our experiment. A simple model of the two-level one-step photo-bleaching well explains the growth of an absorptive grating and the refractive index and also the working wavelength dependence of growth of the refractive grating in the xanthene-dye-doped films.

Effects of high-speed curing devices on shear bond strength and microleakage of orthodontic brackets

This study evaluated the shear-peel bond strength and mode of bond failure of 3 curing devices (plasma arc light, argon laser, and conventional halogen light) and 2 orthodontic bracket adhesives with different filler contents (Transbond XT and Adhesive Precoated [APC]). Observations of microleakage were also reported. Ninety human adolescent premolars were randomly divided into 6 groups, and standardized brackets were bonded according to the manufacturers’ recommendations. The plasma arc light produced significantly ( P = .006) higher bond strength than did the halogen light or the argon laser when Transbond was used. When APC was used, the plasma arc light and the halogen light produced similar results, and they both produced significantly ( P = .015) higher bond strengths than did the argon laser. Overall, the APC showed substantially less variation in bond strength than did the Transbond. Although all curing methods showed significant microleakage ( P < .001), differences among the 3 curing lights occurred only when APC was used. Microscopic evaluations demonstrated that 95% of the specimens failed for adhesion at the bracket or tooth surface; the argon laser produced the highest adhesive remnant index scores. On the basis of bond strength and microleakage results, the plasma arc light was comparable with or superior to the other curing devices, depending on the adhesive used.

The first-order Raman spectra of OsO2

The first-order Raman spectra of the transition metal dioxide OsO2with tetragonal rutile structure have been measured at room temperature. Alinearly polarized argon laser light source and completely oriented single-crystalsamples have made possible unambiguous determination of the four allowedRaman-active phonon modes. Comparison is made with results for other rutilematerials.

Measurement of cytoplasmic calcium concentration in the rods of wild-type and transducin knock-out mice.

A 10 microm spot of argon laser light was focused onto the outer segments of intact mouse rods loaded with fluo-3, fluo-4 or fluo-5F, to estimate dark, resting free Ca(2+) concentration ([Ca(2+)](i)) and changes in [Ca(2+)](i) upon illumination. Dye concentration was adjusted to preserve the normal physiology of the rod, and the laser intensity was selected to minimise bleaching of the fluorescent dye. Wild-type mouse rods illuminated continuously with laser light showed a progressive decrease in fluorescence well fitted by two exponentials with mean time constants of 154 and 540 ms. Rods from transducin alpha-subunit knock-out (Tralpha-/-) animals showed no light-dependent decline in fluorescence but exhibited an initial rapid component of fluorescence increase which could be fitted with a single exponential (tau~1-4 ms). This fluorescence increase was triggered by rhodopsin bleaching, since its amplitude was reduced by pre-exposure to bright bleaching light and its time constant decreased with increasing laser intensity. The rapid component was however unaffected by incorporation of the calcium chelator BAPTA and seemed therefore not to reflect an actual increase in [Ca(2+)](i). A similar rapid increase in fluorescence was also seen in the rods of wild-type mice just preceding the fall in fluorescence produced by the light-dependent decrease in [Ca(2+)](i). Dissociation constants were measured in vitro for fluo-3, fluo-4 and fluo-5F with and without 1 mM Mg(2+) from 20 to 37 degrees C. All three dyes showed a strong temperature dependence, with the dissociation constant changing by a factor of 3-4 over this range. Values at 37 degrees C were used to estimate absolute levels of rod [Ca(2+)](i). All three dyes gave similar values for [Ca(2+)](i) in wild-type rods of 250 +/- 20 nM in darkness and 23 +/- 2 nM after exposure to saturating light. There was no significant difference in dark [Ca(2+)](i) between wild-type and Tralpha-/- animals.

Laser-induced concentric colour domains in a cholesteric liquid crystal mixture containing a nematic azobenzene dopant

The isothermal formation of concentric colour domains has been observed in a cholesteric mixture doped with 10 wt % of a photochromic nematic material. The host cholesteric mixture included the Merck materials BL131a and BL130, while the photochromic dopant was a mixture of 4-n-butyl-4′-n-alkoxyazobenzenes (BAAB). The helical pitch of the host cholesteric mixture was increased, as expected, on addition of the photochromic nematic material prior to irradiation with the molecules in the purely trans-configuration. On irradiation with low power (0.6 mW) argon ion laser light, cis-isomers formed within the interaction region and concentric colour domains appeared. Selective reflection from the colour domains occurred in the 400–560 nm spectral range. The coloured domains persisted in the time period following irradiation and extended beyond the interaction region because of diffusion of the cis-isomers. Using the diffusion equation, an expression has been obtained for the average concentration of cis-isomers in each of the coloured domains and the dependence of the reflection wavelength upon the concentration of cis-isomers has been determined.