Considerable information about the texture of objects can be perceived remotely through a probe. It is not clear, however, how texture perception with a probe compares with texture perception with the bare finger. Here we investigate the perception of a variety of textured surfaces encountered daily (e.g., corduroy, paper, and rubber) using the two scanning modes—direct touch through the finger and indirect touch through a probe held in the hand—in two tasks. In the first task, subjects rated the overall pair-wise dissimilarity of the textures. In the second task, subjects rated each texture along three continua, namely, perceived roughness, hardness, and stickiness of the surfaces, shown previously as the primary dimensions of texture perception in direct touch. From the dissimilarity judgment experiment, we found that the texture percept is similar though not identical in the two scanning modes. From the adjective rating experiments, we found that while roughness ratings are similar, hardness and stickiness ratings tend to differ between scanning conditions. These differences between the two modes of scanning are apparent in perceptual space for tactile textures based on multidimensional scaling (MDS) analysis. Finally, we demonstrate that three physical quantities, vibratory power, compliance, and friction carry roughness, hardness, and stickiness information, predicting perceived dissimilarity of texture pairs with indirect touch. Given that different types of texture information are processed by separate groups of neurons across direct and indirect touch, we propose that the neural mechanisms underlying texture perception differ between scanning modes.
Texture; multidimensional scaling; probe; dissimilarity; roughness; hardness; stickiness
An understanding of texture perception by robotic systems can be developed by examining human texture perception through a probe. Like texture perception through direct touch with the finger, texture perception by indirect means of a probe is multi-dimensional, comprising rough, hard, and sticky texture continua. In this study, we describe the individual subject variability in probe-mediated texture perception, and compare similarities and differences of texture perception between direct touch and indirect touch. The results show variability among subjects, as individual subjects may choose to rely on different degrees of three texture dimensions and do so at different scanning velocities. Despite this variability between scanning conditions within each subject, the subjects make consistently reliable discriminations of textures and subjective magnitude estimates along texture continua when indirectly exploring texture surfaces with a probe. These data contribute information that is valuable to the design of robotic sensory systems, and to the understanding of sensory feedback, which is essential in teleoperations.
sensory feedback; tactile perception; texture; probe; tool
Yellow sticky traps are a common method for monitoring many pests, but it has not been shown whether they could be used as a control method. In this study the impact of yellow sticky traps on the population dynamics of the sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) was determined in the greenhouse and field. In the greenhouse, yellow sticky traps significantly suppressed the population increase of adult and immature whiteflies. The whitefly densities in the greenhouse with traps were significantly lower than the greenhouse without traps. In the field, traps did not have a significant impact on the population dynamics of adult and immature whiteflies. The densities in fields with traps were very similar to fields without traps. These results suggest that yellow sticky traps can be used as an effective method for the control of whiteflies in the greenhouse, but not in the field. This information will prove useful for the effective management of whiteflies in greenhouses.
entire crop growth period; population dynamics
Knowledge of the interactions between mosquitoes and humans, and how vector control interventions affect them, is sparse. A study exploring host-seeking behaviour at a human-occupied bed net, a key event in such interactions, is reported here.
Host-seeking female Anopheles gambiae activity was studied using a human-baited ‘sticky-net’ (a bed net without insecticide, coated with non-setting adhesive) to trap mosquitoes. The numbers and distribution of mosquitoes captured on each surface of the bed net were recorded and analysed using non-parametric statistical methods and random effects regression analysis. To confirm sticky-net reliability, the experiment was repeated using a pitched sticky-net (tilted sides converging at apex, i.e., neither horizontal nor vertical). The capture efficiency of horizontal and vertical sticky surfaces were compared, and the potential repellency of the adhesive was investigated.
In a semi-field experiment, more mosquitoes were caught on the top (74-87%) than on the sides of the net (p < 0.001). In laboratory experiments, more mosquitoes were caught on the top than on the sides in human-baited tests (p < 0.001), significantly different to unbaited controls (p < 0.001) where most mosquitoes were on the sides (p = 0.047). In both experiments, approximately 70% of mosquitoes captured on the top surface were clustered within a 90 × 90 cm (or lesser) area directly above the head and chest (p < 0.001). In pitched net tests, similar clustering occurred over the sleeper’s head and chest in baited tests only (p < 0.001). Capture rates at horizontal and vertical surfaces were not significantly different and the sticky-net was not repellent.
This study demonstrated that An. gambiae activity occurs predominantly within a limited area of the top surface of bed nets. The results provide support for the two-in-one bed net design for managing pyrethroid-resistant vector populations. Further exploration of vector behaviour at the bed net interface could contribute to additional improvements in insecticide-treated bed net design or the development of novel vector control tools.
Bed net; LLIN; ITN; Anopheles gambiae; Two-in-one; Vector behaviour; Mosquito; Malaria; Pyrethroid; Insecticide resistance
In Drosophila, the genes sticky and dFmr1 have both been shown to regulate cytoskeletal dynamics and chromatin structure. These genes also genetically interact with Argonaute family microRNA regulators. Furthermore, in mammalian systems, both genes have been implicated in neuronal development. Given these genetic and functional similarities, we tested Drosophila sticky and dFmr1 for a genetic interaction and measured whole genome expression in both mutants to assess similarities in gene regulation.
We found that sticky mutations can dominantly suppress a dFmr1 gain-of-function phenotype in the developing eye, while phenotypes produced by RNAi knock-down of sticky were enhanced by dFmr1 RNAi and a dFmr1 loss-of-function mutation. We also identified a large number of transcripts that were misexpressed in both mutants suggesting that sticky and dFmr1 gene products similarly regulate gene expression. By integrating gene expression data with a protein-protein interaction network, we found that mutations in sticky and dFmr1 resulted in misexpression of common gene networks, and consequently predicted additional specific phenotypes previously not known to be associated with either gene. Further phenotypic analyses validated these predictions.
These findings establish a functional link between two previously unrelated genes. Microarray analysis indicates that sticky and dFmr1 are both required for regulation of many developmental genes in a variety of cell types. The diversity of transcripts regulated by these two genes suggests a clear cause of the pleiotropy that sticky and dFmr1 mutants display and provides many novel, testable hypotheses about the functions of these genes. As both of these genes are implicated in the development and function of the mammalian brain, these results have relevance to human health as well as to understanding more general biological processes.
The contractile ring is a highly dynamic structure, but how this dynamism is accomplished remains unclear. Here, we report the identification and analysis of a novel Drosophila gene, sticky (sti), essential for cytokinesis in all fly proliferating tissues. sti encodes the Drosophila orthologue of the mammalian Citron kinase. RNA interference–mediated silencing of sti in cultured cells causes them to become multinucleate. Components of the contractile ring and central spindle are recruited normally in such STICKY-depleted cells that nevertheless display asymmetric furrowing and aberrant blebbing. Together with an unusual distribution of F-actin and Anillin, these phenotypes are consistent with defective organization of the contractile ring. sti shows opposite genetic interactions with Rho and Rac genes suggesting that these GTPases antagonistically regulate STICKY functions. Similar genetic evidence indicates that RacGAP50C inhibits Rac during cytokinesis. We discuss that antagonism between Rho and Rac pathways may control contractile ring dynamics during cytokinesis.
cytokinesis; contractile ring; Citron kinase; Rho GTPases; Drosophila
1. Washed erythrocytes, in both acid and alkaline solutions, hemolyze more rapidly when allowed to settle out on a clean microscope slide than when kept in suspension. 2. This is also true on slides coated with paraffin, paraffin oil, or vaseline, and on mica surfaces. 3. The presence of as little as 0.1 per cent serum inhibits such contact hemolysis, particularly in alkaline solutions. 4. Contact hemolysis is most marked on slightly soiled glass, and may occur so rapidly with unfixed cells in a hemocytometer that accurate counts are rendered impossible. 5. Erythrocytes are more sticky than normally in acid solutions and less sticky in alkaline solutions. 6. The increased stickiness of erythrocytes in acid solutions and their larger size during contact hemolysis in acid media provide some experimental evidence for the view that contact hemolysis is to be correlated with an attempt on the part of the corpuscles, or some ingredient of the corpuscle, to spread on the glass after the manner of leucocytes and invertebrate blood cells.
MutS is a DNA repair protein that recognizes unpaired and bulged bases. When it binds to DNA it bends the double helix. We have developed a novel DNA-based nanomechanical device that measures the amount of work that a DNA-bending protein can do when it binds to the double helix. The device we report here is a scissors-like device consisting of two double-crossover (DX) molecules connected to each other by a flexible Holliday junction. The two DX components are connected by a double helix that contains the binding site for MutS; when the binding site duplex is bent, the scissors contracts. The two DX molecules are also joined by sticky ends on an edge adjacent to the binding site; the sticky ends can be disrupted if the protein binds with sufficient free energy. Those sticky ends are flanked by a pair of dyes; when the sticky ends are disrupted, the dyes separate, and the fluorescence resonance energy transfer signal can monitor the disruption. The strength of the sticky ends is readily varied, so that the ability of the protein to disrupt them can be quantitated. We use this device to measure work in conjunction with a second device that measures the bending angle resulting from protein binding, so as to calibrate the system. Our data are in good agreement with previous measurements of MutS binding, indicating that this device is able to measure the strength of binding correctly.
DNA-Based Nanomechanical Devices; Fluorescence Resonance Energy Transfer; DNA Mispairing; DNA Repair; Unusual DNA Motifs
Compounds exhibiting low non-specific intracellular binding or non-stickiness are concomitant with rapid clearing and in high demand for live-cell imaging assays because they allow for intracellular receptor localization with a high signal/noise ratio. The non-stickiness property is particularly important for imaging intracellular receptors due to the equilibria involved.
Three mammalian cell lines with diverse genetic backgrounds were used to screen a combinatorial fluorescence library via high throughput live cell microscopy for potential ligands with high in- and out-flux properties. The binding properties of ligands identified from the first screen were subsequently validated on plant root hair. A correlative analysis was then performed between each ligand and its corresponding physiochemical and structural properties.
The non-stickiness property of each ligand was quantified as a function of the temporal uptake and retention on a cell-by-cell basis. Our data shows that (i) mammalian systems can serve as a pre-screening tool for complex plant species that are not amenable to high-throughput imaging; (ii) retention and spatial localization of chemical compounds vary within and between each cell line; and (iii) the structural similarities of compounds can infer their non-specific binding properties.
We have validated a protocol for identifying chemical compounds with non-specific binding properties that is testable across diverse species. Further analysis reveals an overlap between the non-stickiness property and the structural similarity of compounds. The net result is a more robust screening assay for identifying desirable ligands that can be used to monitor intracellular localization. Several new applications of the screening protocol and results are also presented.
Recruiting and retaining health professions remains a high priority for health system planners. Different employment sectors may vary in their appeal to providers. We used the concepts of inflow and stickiness to assess the relative attractiveness of sectors for physical therapists (PTs) in Ontario, Canada. Inflow was defined as the percentage of PTs working in a sector who were not there the previous year. Stickiness was defined as the transition probability that a physical therapist will remain in a given employment sector year-to-year.
A longitudinal dataset of registered PTs in Ontario (1999-2007) was created, and primary employment sector was categorized as ‘hospital’, ‘community’, ‘long term care’ (LTC) or ‘other.’ Inflow and stickiness values were then calculated for each sector, and trends were analyzed.
There were 5003 PTs in 1999, which grew to 6064 by 2007, representing a 21.2% absolute growth. Inflow grew across all sectors, but the LTC sector had the highest inflow of 32.0%. PTs practicing in hospitals had the highest stickiness, with 87.4% of those who worked in this sector remaining year-to-year. The community and other employment sectors had stickiness values of 78.2% and 86.8% respectively, while the LTC sector had the lowest stickiness of 73.4%.
Among all employment sectors, LTC had highest inflow but lowest stickiness. Given expected increases in demand for services, understanding provider transitional probabilities and employment preferences may provide a useful policy and planning tool in developing a sustainable health human resource base across all employment sectors.
Physical therapy; Health human resources; Workforce
A comparative study of the stabilisation of DNA sticky ends by divalent cations was carried out by atomic force microscopy (AFM), electron microscopy and agarose gel electrophoresis. At room temperature, molecules bearing such extremities are immediately oligomerised or circularised by addition of Mg2+or Ca2+. This phenomenon, more clearly detected by AFM, requires the presence of uranyl salt, which stabilises the structures induced by Mg2+or Ca2+. DNA fragments were obtained by restriction enzymes producing sticky ends of 2 or 4 nucleotides (nt) in length with different guanine plus cytosine (GC) contents. The stability of the pairing is high when ends of 4 nt display a 100% GC-content. In that case, 95% of DNA fragments are maintained circular by the divalent cations, although 2 nt GC-sticky ends are sufficient for a stable pairing. DNA fragments with one blunt end and the other sticky appear as dimers in the presence of Mg2+. Dimerisation was analysed by varying the lengths and concentrations of DNA fragments, the base composition of the sticky ends, and also the temperature. Our observation provides a new powerful tool for construction of inverted dimers, and circularisation, ligation analysis or short bases sequence interaction studies.
Antiplatelet serum (APS) induced an increase in the stickiness of white cells which manifests itself in the increase in number of granulocytes rolling along or sticking to the venous endothelium. Lidocaine treatment prevented the increased stickiness of white cells and, at the same time, the microvascular haemorrhage developing after APS. It can be assumed that increased stickiness of white cells after APS may contribute to endothelial damage.
Jones, Lois M. (University of Wisconsin, Madison), C. R. McDuff, and J. B. Wilson. Phenotypic alterations in the colonial morphology of Brucella abortus due to a bacteriophage carrier state. J. Bacteriol. 83:860–866. 1962.—In the course of examining a number of Brucella cultures with a brucellaphage, it was observed that B. abortus cultures of intermediate colonial morphology, which had a blue-gray colonial appearance, were not lysed within 24 hr; in 48 hr they had developed sticky white growth in the area of the phage drop. When this growth was streaked on agar plates, both white and blue-gray colonies developed. White colonies which were sticky always carried phage and upon restreaking always gave rise to both white and blue-gray colonies. White colonies which were not sticky were rough and phage resistant. Blue-gray colonies produced only blue-gray colonies, did not carry phage, and were similar to the parent in their response to phage. When sticky white colonies were incubated for 6 hr or more in phage antiserum, all phage was eliminated and only blue-gray colonies developed. It was believed that the sticky white colonies were carrier clones in which lysis was delayed until after cell division, thus resulting in the establishment of a colony containing some phage-free progeny. With the accumulation of phage, the colony became sticky. This effect may be caused by the action of bacteriophage enzymes on the cell walls.
Brucellaphage had an extremely slow rate of adsorption on a culture of intermediate colonial morphology. A phage mutant which was more strongly lytic for cultures of intermediate colonial morphology was selected from the original phage. The adsorption rate of this phage was more rapid and the latent period shorter. A serological difference between phages could not be demonstrated.
In a study relating platelet stickiness, plasma fibrinogen and fibrinolysis to fasting plasma lipids in patients with atherosclerosis of the lower limbs, a significant correlation has been observed between platelet stickiness and plasma phospholipid levels. The possible mechanisms are discussed. No other correlation is observed. Fasting levels of plasma fibrinogen were raised, while levels of plasminogen, and the degree of platelet stickiness in many cases were normal.
This study explores how contact angle hysteresis and titling angle relate with stickiness on superhydrophobic surfaces. The result indicates that contact angle hysteresis could not be mentioned as a proper factor to evaluate the surface stickiness. By analyzing the system pinning force of droplet placed on a titled surface, we concluded that both solid fraction and surface geometric factor are the critical factors determining the surface stickiness.
Despite years of research into bipolar disorder (manic depression), its underlying pathophysiology remains elusive. It is widely acknowledged that the disorder is strongly heritable, but the genetics are complex with less than full concordance in monozygotic twins and at least four susceptibility loci identified. We propose that bipolar disorder is the result of a genetic propensity for slow interhemispheric switching mechanisms that become 'stuck' in one or the other state. Because slow switches are also 'sticky' when compared with fast switches, the clinical manifestations of bipolar disorder may be explained by hemispheric activation being 'stuck' on the left (mania) or on the right (depression). Support for this 'sticky' interhemispheric switching hypothesis stems from our recent observation that the rate of perceptual alternation in binocular rivalry is slow in euthymic subjects with bipolar disorder (n = 18, median = 0.27 Hz) compared with normal controls (n = 49, median = 0.60 Hz, p < 0.0005). We have presented evidence elsewhere that binocular rivalry is itself an interhemispheric switching phenomenon. The rivalry alternation rate (putative interhemispheric switch rate) is robust in a given individual, with a test-retest correlation of more than 0.8, making it suitable for genetic studies. The interhemispheric switch rate may provide a trait-dependent biological marker for bipolar disorder.
What type of connectivity structure are we seeing in protein–protein interaction networks? A number of random graph models have been mooted. After fitting model parameters to real data, the models can be judged by their success in reproducing key network properties. Here, we propose a very simple random graph model that inserts a connection according to the degree, or ‘stickiness’, of the two proteins involved. This model can be regarded as a testable distillation of more sophisticated versions that attempt to account for the presence of interaction surfaces or binding domains. By computing a range of network similarity measures, including relative graphlet frequency distance, we find that our model outperforms other random graph classes. In particular, we show that given the underlying degree information, fitting a stickiness model produces better results than simply choosing a degree-matching graph uniformly at random. Therefore, the results lend support to the basic modelling methodology.
protein–protein interaction networks; network models; network properties
Accumulation of thick, sticky mucus is a hallmark of the genetic disease cystic fibrosis (CF) and has a central role in CF pathophysiology. Mutations in the CF transmembrane regulator (CFTR) ion channel are known to result in abnormally thick and sticky mucus; however, why mucus accumulates in CF is still not completely understood. In this issue of the JCI, Garcia and colleagues show that mucin — the heavily glycosylated protein contained within mucus — requires CFTR and bicarbonate in order to be released from mouse intestine (see the related article beginning on page 2613). The authors propose a model whereby CFTR-mediated bicarbonate secretion must be concurrent with mucin exocytosis for proper mucin release.
Background and Aims
Ibicella lutea and Proboscidea parviflora are two American semi-desert species of glandular sticky plants that are suspected of carnivory as they can catch small insects. The same characteristics might also hold for two semi-desert plants with glandular sticky leaves from Israel, namely Cleome droserifolia and Hyoscyamus desertorum. The presence of proteases on foliar hairs, either secreted by the plant or commensals, detected using a simple test, has long been considered proof of carnivory. However, this test does not prove whether nutrients are really absorbed from insects by the plant. To determine the extent to which these four species are potentially carnivorous, hair secretion of phosphatases and uptake of N, P, K and Mg from fruit flies as model prey were studied in these species and in Roridula gorgonias and Drosophyllum lusitanicum for comparison. All species examined possess morphological and anatomical adaptations (hairs or emergences secreting sticky substances) to catch and kill small insects.
The presence of phosphatases on foliar hairs was tested using the enzyme-labelled fluorescence method. Dead fruit flies were applied to glandular sticky leaves of experimental plants and, after 10–15 d, mineral nutrient content in their spent carcasses was compared with initial values in intact flies after mineralization.
Phosphatase activity was totally absent on Hyoscyamus foliar hairs, a certain level of activity was usually found in Ibicella, Proboscidea and Cleome, and a strong response was found in Drosophyllum. Roridula exhibited only epidermal activity. However, only Roridula and Drosophyllum took up nutrients (N, P, K and Mg) from applied fruit flies.
Digestion of prey and absorption of their nutrients are the major features of carnivory in plants. Accordingly, Roridula and Drosophyllum appeared to be fully carnivorous; by contrast, all other species examined are non-carnivorous as they did not meet the above criteria.
Roridula gorgonias; Drosophyllum lusitanicum; Proboscidea parviflora; Ibicella lutea; Cleome droserifolia; Hyoscyamus desertorum; phosphatase; phosphomonoesters; fruit flies; N, P, K, Mg uptake from prey
In a traditional sandwich assay, a DNA target hybridizes to a single copy of the signal probe. Here we employ a modified signal probe containing a methylene blue (a redox moiety) label and a “sticky end.” When a DNA target hybridizes this signal probe, the sticky end remains free to hybridize another target leading to the creation of a supersandwich structure containing multiple labels. This leads to large signal amplification upon monitoring by voltammetry.
The linear rheological properties of networks formed by adding bis-Pd(II) cross-linkers to poly(4-vinylpyridine) (PVP) solution are examined, and the scaling law relationships between the zero shear viscosity (η0) of the networks versus the concentration of PVP solution (CPVP), the concentration of cross-linkers (CX), and the number density of elastically active chains (vphantom) are experimentally determined. The scaling law relationships are compared to the theoretical expectations of the Sticky Rouse and Sticky Reptation models (Macromolecules 2001, 34, 1058-1068), and both qualitative and quantitative differences are observed.
Apolipoprotein (apo) A-I-containing lipoproteins in the form of high density lipoproteins (HDL) are inversely correlated with atherosclerosis. Because HDL is a soft form of condensed matter easily deformable by thermal fluctuations, the molecular mechanisms for HDL remodeling are not well understood. A promising approach to understanding HDL structure and dynamics is molecular dynamics (MD). In the present study, two computational strategies, MD simulated annealing (MDSA) and MD temperature-jump, were combined with experimental particle reconstitution to explore molecular mechanisms for phospholipid (PL)-rich HDL particle remodeling. The N-terminal domains of full length apoA-I were shown to be “sticky”, acting as a molecular latch largely driven by salt bridges, until, at a critical threshold of particle size, the associated domains released to expose extensive hydrocarbon regions of the PL to solvent. The “sticky” N-termini also associate with other apoA-I domains, perhaps being involved in N-terminal loops suggested by other laboratories. Alternatively, the overlapping helix 10 C-terminal domains of apoA-I were observed to be extremely mobile or “promiscuous”, transiently exposing limited hydrocarbon regions of PL. Based upon these models and reconstitution studies, we propose that separation of the N-terminal domains, as particles exceed a critical size, trigger fusion between particles or between particles and membranes, while the C-terminal domains of apoA-I drive the exchange of polar lipids down concentration gradients between particles. This hypothesis has significant biological relevance since lipid exchange and particle remodeling are critically important processes during metabolism of HDL particles at every step in the anti-atherogenic process of reverse cholesterol transport.
The aqueous extract of flowers of I. coccinea was evaluated for its cytotoxic and mutagenic effects on the meristematic cells of onion root tip. The percentage of abnormalities was found to increase with the increase in the concentration of the extract from 20 to 60 mg/ml. With 80 mg/ml completed arrest or total inhibition of cell division was observed. The major abnormalities were unprinted chromosomes at metaphase. Stickiness and clumping of chromosomes were induced by higher concentrations of the extract. Sticky anaphase bridges and formation of micronuclei were induced at the highest concentration (80mg/ml) tried. The significance of these abnormalities is discussed in detail. The results point to the potential use of the aqueous extract of flowers of I. coccinea in the chemotherapy of cancer.
Regulated RhoA localization at the cleavage site is mediated by the Sticky/Citron kinase and ensures RhoA’s proper activation and appropriate contractile ring dynamics during cytokinesis.
In many organisms, the small guanosine triphosphatase RhoA controls assembly and contraction of the actomyosin ring during cytokinesis by activating different effectors. Although the role of some RhoA effectors like formins and Rho kinase is reasonably understood, the functions of another putative effector, Citron kinase (CIT-K), are still debated. In this paper, we show that, contrary to previous models, the Drosophila melanogaster CIT-K orthologue Sticky (Sti) does not require interaction with RhoA to localize to the cleavage site. Instead, RhoA fails to form a compact ring in late cytokinesis after Sti depletion, and this function requires Sti kinase activity. Moreover, we found that the Sti Citron-Nik1 homology domain interacts with RhoA regardless of its status, indicating that Sti is not a canonical RhoA effector. Finally, Sti depletion caused an increase of phosphorylated myosin regulatory light chain at the cleavage site in late cytokinesis. We propose that Sti/CIT-K maintains correct RhoA localization at the cleavage site, which is necessary for proper RhoA activity and contractile ring dynamics.
Among trapping mechanisms in carnivorous plants, those termed ‘active’ have especially fascinated scientists since Charles Darwin’s early works because trap movements are involved. Fast snap-trapping and suction of prey are two of the most spectacular examples for how these plants actively catch animals, mainly arthropods, for a substantial nutrient supply. We show that Drosera glanduligera, a sundew from southern Australia, features a sophisticated catapult mechanism: Prey animals walking near the edge of the sundew trigger a touch-sensitive snap-tentacle, which swiftly catapults them onto adjacent sticky glue-tentacles; the insects are then slowly drawn within the concave trap leaf by sticky tentacles. This is the first detailed documentation and analysis of such catapult-flypaper traps in action and highlights a unique and surprisingly complex mechanical adaptation to carnivory.