Characterization of Odorous Compounds in Rotten Blue-green Algae

An ice-nucleating bacterium, strain KUIN-1, was isolated from the leaves of field beans (Phaseolus vulgaris L.). Strain KUIN-1 was identified as Pseudomonas fluorescens from its taxonomical characteristics. Ice-nucleating activity was obtained when strain KUIN-1 was cultured aerobically in a medium containing Koser citrate broth (pH 7.0) for 24 hr at 18°C. The ice- nucleating activity did not appear until the bacterial cell concentration reached 10⁷ to 10⁸/ml. Nucleation at — 3.0°C was detected in suspensions (1.8 × 10⁹ cells/ml) of cells that had been grown on the medium containing Koser citrate broth. Strain KUIN-1 produced a lower nucleation frequency (i.e. the number of ice nuclei/cell) than did ice-nucleating Pseudomonas syringae No. 31 suspensions, particularly at temperatures above — 5°C. The nucleation frequency of strain KUIN- 1-suspensions was similar to that obtained for an ice-nucleating Erwinia herbicola No. 26 at — 5°C.     

Gamma Irradiation on Fermentation Mashes Consisting Mainly of Cane Molasses

The application of the radiopasteurization method to fermentation media consisting mainly of molasses was investigated. γ-Irradiation was found to have an excellent pasteurization effect on the fermentation media and at the same time to bring about an increase in the fermentation rate and yield of ethanol. Percent survivals in molasses decreased to ca. 70% by heating at 80°C for 30 min, to ca. 10% by irradiation with 3.0 × 10⁵ rad and to ca. 1% by 6.0 × 10⁵ rad. Irradiated mash was suitable for the medium of the “starter”, since the rate and the degree of the growth of Saccharomyces cerevisiae in irradiated mash did not differ from those of the growth in heat-pasteurized mash.

In the case of the molasses mash supplemented with nitrogen sources, the fermentation rate and yield of ethanol in irradiated mash were larger than those in heated mash. Besides, in the absence of nitrogen sources a 14% difference in fermentation yield was seen between the mash irradiated with 3.0 × 10⁵ rad and the mash heated at 80°C. With the doses ranging from 1.0 × 10⁵ to 9.5 × 10⁵ rad, concentrations of total sugar and direct reducing sugar, pH, and optical density of molasses were little affected by irradiation.     

DIFFERENCES IN THE NUCLEAR RIBONUCLEIC ACID CONTENT IN DIFFERENT AREAS OF THE HUMAN ADULT AND FOETAL BRAIN*

Abstract— Four different areas of ten brains from adults in the age group between 44 and 74 years and two areas of six foetal brains were studied. The cellular density was similar in the different areas of the brain of adult man; it averaged 11.9 × 10⁷/g wet tissue. The number of neurons per g wet tissue varied from 2.22 × 10⁷ in the cortex to 0.15 × 10⁷ in the centrum semiovale. In the brain of adults the overall RNA content of nuclei was higher for the cortex than for the corpus callosum or the centrum semiovale. The RNA content of neuronal nuclei was higher than that of non-neuronal nuclei. In the brain of foetuses the nuclear density was higher than in adults. The DNA content of a nucleus in foetal brain was 2–3 times as high as in adult brain and it approached adult values with increasing maturity.     

Development of isolation and cultivation method for outer root sheath cells from human hair follicle and construction of bioartificial skin

Obtaining a sufficient amount of healthy keratinocytes from a small tissue is difficult. However, ORS cells can be a good source of epithelium since they are easily obtainable and patients do not have to suffer from scar formation at donor sites. Accordingly, the current study modified the conventional primary culture technique to overcome the low propagation and easy aging of epithelial cells during culturing. In a conventional primary culture, the average yield of human ORS cells is 2.1×10³ cells/follicle based on direct incubation in a trypsin (0.1%)/EDTA (0.02%) solution for 15 min at 37°C, however, our modified method was able to obtain about 6.9×10³ cells/follicle using a two-step enzyme digestion method involving dispase (1.2 U/mL) and a trypsin (0.1%)/EDTA (0.02%) solution. Thus, the yield of primary cultured ORS cells could be increasd three times higher. Furthermore, a total of 2.0×10⁷ cells was obtained in a serum-free medium, while a modified E-medium with mitomycin C-treated feeder cells produced a total of 6.3×10⁷ cells over 17 days when starting with 7.5×10⁴ cells. Finally, we confirmed the effectiveness of our ORS cell isolation method by presenting their ability for reconstructing the bioartificial skin epitheliumin vitro     

Presence de glycosyltransferases a accepteurs chromatiniens dans les membranes nucleaires d'hepatocytes de singeThe presence of glycosyltransferases on chromatin acceptors in monkey liver nuclear membranes

Nuclei were prepared from monkey hepatocytes by centrifugation of the homogenate on a cushion of 2.3 M sucrose, during 45 min at 100 000 × g. The yield was 2.2 · 10⁷ nuclei per g of liver, and 70% of the homogenate DNA was recovered in these nuclei. An electron microscopic study as well as a biochemical analysis of marker enzymes showed that the nuclei are not contaminated by other subcellular fractions, especially endoplasmic reticulum. A mannosyltransferase and an N-acetylglucosaminyltransferase, working on endogenous glycoproteic acceptors, are present in the nuclei for 1.4 and 6.5% of the homogenate activities, respectively.The nuclei are hydrolysed by DNAase I. The suspension, adjusted in 1.9 M sucrose, was centrifuged for 2 h at 100 000 × g, under a buffer layer. Purified nuclear membranes were collected at the interface. These membranes did not contain any more endoplasmic reticulum enzyme activities, but the mannosyl and N-acetylglucosaminyltransferase activities were still present. They essentially work on an exogenous chromatin acceptor, prepared by lysis of the nuclei. The eventual role of these glycosyltransferases in the glycosylation of non-histone proteins is discussed.     

Yield performance of 14 novel inter- and intra-species Miscanthus hybrids across Europe

Miscanthus, a C4 perennial rhizomatous grass from Asia is a leading candidate for the supply of sustainable biomass needed to grow the bioeconomy. European Miscanthus breeding programmes have recently produced a new range of seeded hybrids with the objective of increasing scalability to large acreages limited by current clonal propagation. For the EU-GRACE project, new replicated field trials were established in seven locations across Europe in 2018 with eight intraspecific M. sinensis hybrids (sin × sin) and six M. sacchariflorus × M. sinensis (sac × sin) from Dutch and UK breeding programmes, respectively, with clonal Miscanthus × giganteus. The planting density of the sin × sin was double that of sac × sin (30,000 & 15,000 plants ha⁻¹), creating commercially relevant upscaling comparisons between systems. Over the first 3 years, the establishment depended on location and hybrid. The mature sin × sin hybrids formed tight tufts of shoots up to 2.5 m tall which flower and senesce earlier than the taller sac × sin hybrids. Following the third growing season, the highest yields were recorded in Northern Italy at a low altitude (average 13.7 (max 21) Mg DM ha⁻¹) and the lowest yielding was on the industrially damaged marginal land site in Northern France (average 7.0 (max 10) Mg DM ha⁻¹). Moisture contents at spring harvest were lowest in Croatia (21.7%) and highest in Wales, UK (41.6%). Overall, lower moisture contents at harvest, which are highly desirable for transport, storage and for most end-use applications, were found in sin × sin hybrids than sac × sin (30% and 40%, respectively). Yield depended on climate interactions with the hybrid and their associated planting systems. The sin × sin hybrids appeared better adapted to northern Europe and sac × sin hybrids to southern Europe. Longer-term yield observations over crop lifespans will be needed to explore the biological (yield persistence) and economic costs and benefits of the different hybrid systems.     

Levels of aflatoxin B1, bacteria and fungi in feed and food in 1971 — 1987

Totally 39% out of 8371 feed and their component samples were contaminated by aflatoxin B₁. Mean contamination was 36μg/kg with maximum yield 10100 μg/kg. Contamination of samples by total count of organisms, mean contamination and maximum yield, respectively was: 1) bacteria 99%, 2.2×10⁶, 2.4×10⁸; 2) proteolytic bacteria 94%, 1.2×10⁵, 3.0×10⁶;3) moulds 98%, 1.3×10⁵, 9.0×10⁶; 4) yeasts 44 %, 3.3×10⁴, 3.6×10⁶. The samples were contaminated in 92 % byAspergillus spp, in 71% byAspergillus flavus, in 83% byPenicillium spp, and in 20% byFusarium spp with mean contamination 8.3×104, 1.1×10³, 4.2×10⁴, 5.0×10³ , and maximum yield 6.8×10⁶, 1.0×10⁵, 5.0×10⁶, 1.5×10⁶, respectively. Totally 8.5% of strains were aflatoxinogenic and 4.4% of the strains were isolated from feed and 21 % of the strains from grain/nut.     

Purification and Characterization of Beauveria bassiana Proteinases

Two chymotrypsin‐like serine proteinases are produced by B. bassiana 278 when grown on different carbon and nitrogen sources. By employing acetone precipitation, gel filtration and ion‐exchange chromatographies, the enzymes were separated from the culture filtrate after propagation of the fungus on medium enriched either with ground larvae of Apis mellifera (Proteinase I) or porcine blood plasma (Proteinase II). The purified enzymes with a molecular mass of approximately 32 kDa hydrolyzed natural protein substrates: casein, hide powder azure (HPA), azocoll and much less elastin Congo Red and collagen. They differ from each other in the optimum pH value, amino acid composition, Michaelis constant and susceptibility to natural chymotrypsin inhibitors. Both proteinases hydrolyze suc‐Ala‐Ala‐Pro‐Phe‐p‐NA with an apparent K_m of 2.03 × 10^—3 M and 1.04 × 10^—4 M, respectively. The turkey ovomukoid (OMTKY) and cathepsin G/chymotrypsin inhibitor inhibit only Proteinase II from the larvae hemolymph of Apis mellifera (AMCI). The association constant of the interaction of this enzyme with AMCI was estimated to be very high (4.11 × 10⁹ M^—1).     

Quantitative and qualitative aspects in the production of a nuclear polyhedrosis virus in Spodoptera exigua larvae

Spodoptera exigua nuclear polyhedrosis virus was produced in late fourth instar S. exigua larvae, reared on semi-artificial diet. A maximum amount of virus, 1–2 × 10⁹ polyhedra/larva, was produced in individually-reared larvae after 7 days of incubation, with an inoculum of 7–5 × 10⁴ polyhedra/cm² diet surface. Virus yield was slightly reduced to 9 × 10⁸ polyhedra/larva when production was carried out in groups of 400 and 600 larvae per container. Biological activity of virus harvested from living larvae and from dead cadavers was similar. Microbial contaminants, predominantly bacteria, in the virus product numbered 1–6% of the number of polyhedra. Tests for the presence of vertebrate-pathogenic bacteria in the virus product were all negative.     

Electron microscopy of human interphase nuclei

Quantitative electron microscopy was used to analyze surface-spread, critical-point-dried human interphase nuclei and chromatin. The following information is presented: (1) Unstimulated interphase nuclei of lymphocytes from peripheral blood have a mean dry mass of 50.30×10^?12 g. The mean dry mass of stimulated nuclei of lymphocytes was determined to be 59.34×10^?12 g, a significant statistical difference from the unstimulated ones. (2) Mean diameter of chromatin fibers and mean fiber mass per micron were 199ű15% coefficient of variation (C.V.) and 5.95×10^?16g×29% C.V., respectively. (3) A line of regression of fiber mass on fiber diameter for 83 fibers indicated that a 200-Å fiber has a mass of 5.86×10^?16g/μ, or almost the same as the mean fiber mass of 5.95× 10^?16g/μ. (4) With the value 7×10^?12g for the DNA content of an unstimulated lymphocyte nucleus, a total length of 215 cm is calculated for the DNA double helix. When this length is compared to the mean length of chromatin fiber per nucleus (7.59 cm), a ratio of 28.3 to 1 results, which is called the DNA-packing ratio. (5) This DNA-packing ratio of 28.3 is reasonably close to the packing ratio of 26.9 suggested from model calculations for the second DNA supercoil in a 200-Å chromatin fiber.     

INHIBITION OF ACETYLCHOLINESTERASE IN VITRO BY PENTYLENETETRAZOL1

Abstract—The effect of pentylenetetrazol (PTZ) on acetylcholinesterase (E.C.3.1.1.7) was studied in vitro. The kinetics of the reaction were studied on AChE in crude homogenates of rat brain and in purified preparations from Electrophorus electricus. The K_m for rat brain AChE was 1·22 × 10^-4m, with a V_max of 1·37 μmol/g/min whereas the K₄ for competitive inhibition of the enzyme by PTZ was 4·7 × 10^-3m. The commercially purified enzyme exhibited a K_m of 1·73 × 10^-4m and a K_i of 1·00 × 10^-3m.     

Comparison of Archaeal Populations in Soil and Their Encapsulated Iron-Manganese Nodules in Four Locations Spanning from North to South China

To characterize the archaeal community composition in soil originating iron-manganese nodules, four types of soils—brown soil, yellow-cinnamon soil, yellow brown soil and red soil—and their associated iron-manganese nodules were collected from Queyu (QY), Zaoyang (ZY), Wuhan (WH) and Guiyang (GY), China, respectively, and subjected to quantitative polymerase chain reaction, cloning and sequencing analyses. The results showed that the archaeal 16S rRNA gene copy numbers in nodules, ranging between 3.59 × 10² and 4.17 × 10³ copies g^?1 dry nodule, were about 50–1000 times lower than those in their corresponding soils (1.87 × 10⁵ to 1.08 × 10⁶ copies g^?1 dry soil), correlating with the low organic matter in the nodules, while archaea accounted for a relatively higher proportion of total prokaryote in nodules than in soils. Community composition analysis suggested that the archaeal diversity in both soils and nodules were much lower than bacterial, but archaeal community structures were similar to each other among the soils and nodules from the same location but varied among four locations, converse to the previous observation that bacterial community shifted markedly between nodules and soils as the result of habitat filtering. The archaeal communities in both soils and nodules were predominated by Thaumarchaeota Group I.1b with the relative abundance ranging between 73.88 and 94.17%, except that Euryarchaeota dominated the archaeal community in one nodule sample (WHn) developed from lake sediment. The finding shed new light on the archaeal diversity and their ecophysiology in different habitats, and further supported the opinion that archaea are more adaptable to stress and unfavorable conditions.     

MEMBRANE THIAMINE TRTPHOSPHATASE FROM RAT BRAIN: INHIBITION BY ATP AND ADP

—The hydrolysis of ThTP by rat brain membrane-bound ThTPase is inhibited by nucleoside diphosphates and triphosphates. ATP and ADP are most effective, reducing hydrolysis by 50% at concentrations of 2 × 10^?5m and 7·5 × 10^?5m respectively. Nucleoside monophosphates and free nuclcosides as well as P_i have no effect on enzyme activity. ThMP and ThDP also fail to inhibit hydrolysis in concentrations up to 5 × 10^?3m . Non-hydrolysable methylene phosphate analogs of ATP and ADP were used in further kinetic studies with the ThTPase. The mechanism of inhibition by these analogs is shown to be of mixed non-competitive nature for both compounds. An observed K_i, of 4 × 10^?5m for the ATP analog adenosine-PPCP and 9 × 10^?5m for the ADP analog adenosine-PCP is calculated at pH 6·5. Formation of the true enzyme substrate, the [Mg²⁺. ThTP] complex, is not significantly affected by concentrations of analogs producing maximal (>95%) inhibition of enzyme activity. Likewise the relationships between pH and observed K_m and pH and V_max are not shifted by the presence of similar concentrations of inhibitor.     

Seeding tallgrass prairie in monospecific patches promotes native species establishment and cover

In tallgrass prairie reconstruction, the way desired seeds are arranged on the landscape may affect species establishment, species persistence, and the establishment and persistence of undesired (nonseeded) species from the local propagule pool. To test effects of species seeding pattern on how grasslands develop spatially, we seeded 20—4 × 4–m bare soil plots with 16 tallgrass prairie species. Treatment plots were divided into 16—1 × 1–m subplots, 64—0.5 × 0.5–m subplots, 256—0.25 × 0.25–m subplots, or 1,024—0.125 × 0.125–m subplots. Each species was hand broadcast into separate subplots (1 m² total area/species) within each plot. An additional treatment included uniformly mixing and broadcasting all seeds across a plot. We recorded species cover at the 0.125 × 0.125–m scale within each plot at the beginning of the second and third growing seasons. While species persistence was greatest within plots seeded with larger subplots, plots with smaller subplots were more spatially diverse and less occupied by nonseeded species over time than larger subplot and mixed plots. As is common in reconstruction efforts, establishment was variable among species and seeding with monospecific subplots enhanced colonization of desired rhizomatous species (e.g., Heliopsis helianthoides, Monarda fistulosa, Elymus virginicus) into unoccupied locations at the expense of species from the local propagule pool. Results suggest that seeding species in smaller, monospecific patches could result in grasslands with a more balanced native species composition than those established with a seed mixture approach.     

Extraction and characterisation of alginate from brown seaweeds (Fucales,Phaeophyceae) collected from Port Dickson,Peninsular Malaysia

Four species of brown seaweeds, namely Sargassum baccularia, Sargassum binderi, Sargassum siliquosum and Turbinaria conoides, harvested from Port Dickson, Negeri Sembilan, Malaysia were analysed for ash content, alginate yield and alginate properties. Seaweeds calcined at 450°C were found to have low amount of non-combustible residue as these were not contaminated by calcareous animals. Alginate was extracted from these seaweeds by two methods: hot and cold. In the hot method, the storing time was 3 h and the processing temperature was 50°C, whilst in the cold method, the sample was stored overnight at room temperature. Higher yield of alginate was obtained by the hot method compared to the cold method, but alginate extracted by the cold method gave higher molecular weight. In the hot method, 49.9% of alginate was extracted from S. siliquosum, followed by T. conoides (41.4%), S. binderi (38.9%) and S. baccularia (26.7%). Alginate extracted from T. conoides has an average molecular weight, M _w, of 8.06 × 10⁵ g mol⁻¹, whereas alginate from S. siliquosum was the lowest in M _w (4.81 × 10⁵ g mol⁻¹) when the extraction was done at room temperature. Alginate extracted from S. baccularia was found to be very heat-sensitive. Its M _w has dropped more than 83%, from 7.52 × 10⁵ to 1.23 × 10⁵ g mol⁻¹, when the extraction temperature was raised. The effect of heat on the extent of depolymerisation of the alginate molecule of the other three brown seaweed species was less significant, with decrease in molecular weight ranging between 13% and 16%.     

THE CYTOLOGY AND PHYLOGENETICS OF THE DIPLOID SPECIES OF GOSSYPIUM

Meiotic chromosome behavior of 11 inter-genomic hybrids of Gossypium (2n = 26) were investigated. Per cell univalent frequencies at meiotic metaphase I in these hybrids were: A genome × Cgenome—G. herbaceum × sturtianum, 10.53; G. herbaceum × australe, 18.05. A genome × E genome—G. smnalense × arboreum, 21.82. B genome × C genome—G. anomalum × sturtianum, 9.23; G. anomalum × australe, 13.11. B genome × D genome—G. anomalum × klotzschianum, 17.45; G. anomalum × raimondii, 18.83. C genome × D genome—G. robinsonii × davidsonii, 12.77; G. sturtianum (armourianum × thurberi), 8.63. C genome × E genome—G. somalense × australe, 23.78; G. somalense × bickii, 25.58. Trivalent and quadrivalent frequencies were relatively high for those hybrids involving a C genome species, indicating that a reciprocal translocation differentiates the C genome from the A, B, D, and E genomes. The results of this study and the data of similar studies cited from the literature on Gossypium cytogenetics are discussed relative to the phylogenetics and evolution of the major (genome) groups of Gossypium and their constituent taxa.     

Resistance to Water Transfer in Desert Shrubs Native to Death Valley, California

Differences in plant resistance to water flow, patterns of water transport through stems, and stomatal behavior were studied on three species native to the exceptionally hot and dry habitat of Death Valley, California (—, and Larrea divaricata). Dawn xylem water potentials in July for Atriplex were — 27.5 bar under natural conditions. Corresponding values for Tidestromia and Larrea were respectively — 8.0 bar and -32.0 bar (natural) and — 7.5 bar and — 18.0 bar (irrigated). Recovery of xylem water potential in covered field plants of an irrigated transplant garden reached a maximum value in July of — 9.5 bar in Atriplex, — 5.7 bar in Tidestromia and — 7.0 bar in Larrea. Resistance to free-energy transfer was used to study resistance to water transport through the plants. Under field conditions irrigated Atriplex plants gave a whole plant resistance of 20.70 × 10⁶ s cm^-1, as compared lo 18.37 × 10⁶ s cm^-1 for Larrea and 10.01 × 10⁶ s cm^-1 for Tidestromia. Plant resistance to water How computed by this method on Atriplex plants grown under laboratory conditions gave a value of 3.73 × 10⁶ s cm^-1 at 35C. Paths of water flow in field plants as investigated with injected acid fuchsin indicated a sectorial straight type vessel. The relationship between transpiration rates and xylem water potentials in Atriplex hymenelytra was linear between transpiration 1.28 μg cm^-2 s^-1 and 2.35 μg cm^-2 s^-1 at 35°C. These results indicate that according to the Van den Honert model for water transport, plant resistance to water flow remained rather constant at this temperature. In Atriplex grown under laboratory conditions there was an adjustment of plant resistance so change in water flux at 9.5°C and 25°C. When laboratory-grown plants of Atriplex and Tidestromia were subjected to water stress by withholding water. Tidestromia closed stomata and reduced transpiration rates at higher water potentials than in Atriplex. The ratio of vapor pressure gradients of leaf/air to leaf diffusion resistance was proportional lo transpiration rates. It is suggested that Atriplex hymenelytra is a species that combines strong regulation of water loss by stomata with low efficiency of the water transport system. These plants are unable to prevent depression of plant water potential as transpiration increases. On the other hand. Tidestromia oblongifolia has little stomatal regulation of transpiration and a highly efficient water transport system. These plants sustain very high rates of transpiration without significant decrease in plant water potential.     

Yields of Miscanthus × giganteus and Panicum virgatum decline with stand age in the Midwestern USA

For the C4 perennial grasses, Miscanthus × giganteus and Panicum virgatum (switchgrass) to be successful for bioenergy production they must maintain high yields over the long term. Previous studies under the less conducive climate for productivity in N.W. Europe found little or no yield decline in M. × giganteus in the long term. This study provides the first analysis of whether yield decline occurs in M. × giganteus under United States. Midwest conditions in side‐by‐side trials with P. virgatum over 8–10 years at seven locations across Illinois. The effect of stand age was determined by using a linear regression model that included effects of weather. Miscanthus × giganteus produced yields more than twice that of P. virgatum averaging 23.4 ± 1.2 Mg ha^?1 yr^?1 and 10.0 ± 0.9 Mg ha^?1 yr^?1, respectively, averaged over 8–10 years. Relationships of yield with precipitation and growing degree days were established and used to estimate yields corrected for the stochastic effects of weather. Across all locations and in both species, yield initially increased until it reached a maximum during the fifth growing season and then declined to a stable, but lower level in the eighth. This pattern was more pronounced in M. × giganteus. The mean yields observed over this longer term period of 8–10 years were lower than the yields of the first 5 years. However, this decline was proportionately greater in M. × giganteus than in P. virgatum, suggesting a stronger effect of stand age on M. × giganteus. Based on the average yield over the period of this study, meeting the United States Renewable Fuel Standard mandate of 60 billion liters of cellulosic ethanol by 2022, would require 6.8 Mha of M. × giganteus or 15.8 Mha of P. virgatum. These appear manageable numbers for the United States, given the 16.0 Mha in the farmland Conservation Reserve Program in addition to another 13.0 Mha abandoned from agriculture in the last decade.     

Interaction of Kinetin and Indoleacetic Acid in the Avena Straight-Growth Test

Kinetin has a stimulating effect in the Avena straight-growth test. The action of different concentrations of kinetin, 2.5 × 10^?7, 2.5 × 10^?6 and 2.5 × 10^?5M, in combination with different concentrations of IAA was studied in this test. It was shown that the effect of low IAA concentrations, 0.25 × 10^?7 and 1 × 10^?7M, was strongly enhanced by the addition of all the kinetin concentrations investigated. The effect of the highest IAA concentrations, 25 × 10^?7 and 100 × 10^?7M, on the other hand, was inhibited relatively strongly by the highest employed concentration of kinetin. The results are explained as due to a kinetin-produced increase of auxin in the coleoptile segment, which in combination with low IAA concentrations can lead to a growth stimulation and with high IAA concentrations to a growth inhibition. Since kinetin in purification and chromatography of auxin can partly follow IAA, thereby affecting the quantitative yield, it is emphasized that, prior to the test, auxin extracts containing cytokinins should be freed from the latter by, for example, gel filtration or paper electrophoresis.