Astrophysicist studies black hole collisions and neutron star mergers

When IMRE BARTOS first became interested in researching gravitational waves in 2004, his college professors advised against it. Since Albert Einstein theorized about their existence in 1915, no one had actually observed gravitational waves, ripples in space time caused by major cosmic events such as black hole collisions. The field was considered a dead end.

That continued to be true for another decade — until September 14, 2015, when, using an algorithm designed at UF, an international team of researchers detected gravitational waves emanating from the collision of two black holes over a billion light years from Earth. Arriving a century after Einstein’s prediction, the discovery shocked Bartos, then at Columbia University.

“It took me several days to fathom this was real,” Bartos said. Thankfully, he had ignored his skeptical professors’ advice and focused his research on an area of study that was about to blossom. That research eventually brought him to UF, where he became an assistant professor in 2017.

Gambling on this exciting field has continued to pay off for Bartos: The Alfred P. Sloan Foundation announced Wednesday that Bartos is the recipient of the 2020 Sloan Research Fellowship. The two-year Fellowship, which comes with an award of $150,000, recognizes researchers for “distinguished performance and a unique potential to make substantial contributions to their field.”

For Bartos, the Fellowship is an indication that the scientific community values not only his own research but the study of gravitational waves at large.

“It is very reassuring,” he said. “This award means the community has trust in me to use these resources to find exciting new cosmic events.”

The research fellowship, which is not tied to a specific project, affords him flexibility to pursue the latest discoveries in his field.

“Especially in a field that is very new with many interesting opportunities, it is critical to focus on the most pressing, riskier questions that may be arising very quickly,” Bartos said. “In a five-year period, there have been a number of complete pivots in the direction of the field.”

Five years after the very first detection of gravitational waves, researchers are now identifying one black hole collision a week. Bartos estimates that in two years, the rate will be one per day. In addition to black hole collisions, Bartos dedicates much of his research to the study of neutron star mergers, which produced the reserves of gold, platinum, uranium and many other heavy elements found on Earth.

“We’re starting to discover things that are changing how we think about the universe,” he said.

There are few better places to pursue this research than UF, one of the key institutions in the LIGO (Laser Interferometer Gravitational-Wave Observatory) collaboration that has been behind the field’s major discoveries. At UF, Bartos said he has access to expert collaborators, advanced instrumentation, a supportive research environment and elite students.

While his areas of interest might seem remote to us on Earth, Bartos believes that cosmic events offer insight into fundamental laws of nature in ways that can’t be observed terrestrially. For example, while physicists have made new discoveries using particle accelerators, black holes can accelerate particles up to more than a billion times faster.

“Very often in science and in physics in particular we can learn more about what is really behind different phenomena by looking at extremes,” he said. “For that, we very often need to go beyond Earth and even beyond the Solar System.”

GAINESVILLE — The National Endowment for the Humanities (NEH) announced Tuesday, January 14, that two UF College of Liberal Arts faculty have received fellowships to pursue projects in history and anthropology.

Lillian Guerra

LILLIAN GUERRA, professor in the Department of History, was awarded $60,000 from the NEH to research youth education programs during the Cuban Revolution between 1961 and 1981. AMANDA CONCHA-HOLMES, courtesy faculty in the Department of Anthropology, received $50,000 to conduct a digital ethnography of the Silver River in Florida.

Guerra said she was thrilled by the news. Her project, which will become a book entitled Patriots and Traitors in Cuba: Political Pedagogy, Rehabilitation and Vanguard Youth, 1961-1981, uses oral history and archival research to explore how the Cuban state aimed to rid the country of those lacking “revolutionary genes” by framing children as either patriots or traitors. The book will be her fifth, following previous historical works about Puerto Rico and Cuba.

“Of all of the books I have researched on Cuba, this is surely the most personal and intimate in the questions it asks and the stories it tells,” she said. “The NEH has made it possible for me to take the time to make multiple generations of Cubans’ complex and often painful history come alive.”

Amanda Concha-Holmes

Concha-Holmes’ project is titled Who belongs? Evocative Ethnography to Interpret Being, Belonging and Becoming on the Borderlands of Florida’s Silver River. She is using a digital, interactive platform featuring documentary video, photography, audio and more to reveal “multifaceted historical, cross-cultural and multispecies layers” of the Silver River.

“The funding of the National Endowment for the Humanities Mellon Fellowship for Digital Publication will allow me to fully focus on crafting this multimodal manuscript, which looks at the Silver River as a protagonist through multiple temporal and cultural perspectives,” Concha-Holmes said. “It is ultimately about being, becoming and belonging, which is relevant to all of us.”

The awards were among $30.9 million in grants distributed by the NEH to 188 humanities projects, spanning 45 states and the District of Columbia.

In the epicenter of the Zika epidemic in northeast Brazil, 73 percent of people living in an urban slum in Salvador were infected in 2015. However, in this highly affected population, those with immunity to dengue, a genetically similar virus, had a reduced risk of infection with Zika. University of Florida epidemiologist Derek Cummings is a senior author on the first study to explore the relationship between dengue antibodies and Zika resilience. This new research, published in Science on Feb. 8, 2019, offers insights into how immunity might be conferred from dengue-infected individuals exposed to Zika. “This study is the first to demonstrate that immunity to dengue can protect against Zika infection in human populations,” said Cummings, professor of Biology and faculty in the Emerging Pathogens Institute.

Led by the Brazilian Ministry of Health, a team including Cummings, as well as scientists from the Yale School of Public Health and the University of California San Francisco, examined a cohort of 1,453 residents participating in a long-term health survey in Pau da Lima, Salvador, Brazil. The residents may have been exposed to Zika during the 2015 outbreak in northeastern Brazil. The team then examined a subset of 642 dengue-infected residents and analyzed their risk for Zika. “Even though there was protective immunity in the population, this community was heavily infected,” said Cummings. “We estimate that 73 percent of the population was infected by Zika.”

The team developed a unique assay that measured immunoglobulin G3, which responds to a key protein in Zika. Despite the study area comprising less than one-quarter of a square kilometer, the researchers found an overall attack rate of 73 percent, yet wide variation in the risk of Zika infection across short distances. Likely depending on environmental factors such as mosquito breeding grounds, rates of infection varied from a low of 29 percent to a high of 83 percent.

Out of the 642 samples, 86 percent were positive for dengue, and for those with this prior immunity to dengue, each doubling of antibody titers was associated with a 9 percent reduction in risk of Zika infection.
“Although there are pockets of susceptible populations which were not hit by Zika, the Zika pandemic has created overall high rates of immunity in the Americas, which will be a barrier for outbreaks for the next few years,” said Cummings.

The study was supported by the US National Institutes of Health (grant to the University of Florida NIAID R01 AI114703, other institutes supported by NIAID R01 AI121207, NIAID U01 AI088752, FIC R01 TW009504 and FIC R25 TW009338), Yale School of Public Health and the Brazilian Ministries of Health, Education and Science and Technology.

Surrounded by salty water, sea snakes sometimes live a thirsty existence. Previously, scientists thought that they were able to drink seawater, but recent research has shown that they need to access freshwater. A new study published in PLOS ONE on Feb. 7 and led by Harvey Lillywhite, professor of biology of the University of Florida, shows that sea snakes living where there is drought relieve their dehydration as soon as the wet season hits, and do so by obtaining freshwater from “lenses” that form on the surface of the ocean during heavy rain—events in which the salinity at the surface decreases enough for the water to be drinkable.

The yellow-bellied sea snake (Hydrophis platurus) is the only reptile in the order Squamata that lives on the open sea. It has one of the largest geographic ranges of any vertebrate species. Given its broad range and seafaring existence, during the dry season (6-7 months at the study site in Costa Rica) it has no access to freshwater. How they survive in regions of drought seems to hinge upon access to freshwater lenses, but little is known about how marine vertebrates react to or consume rainfall. “This study contributes to a fuller understanding of how pelagic sea snakes, and possibly other marine animals, avoid desiccation following seasonal drought at sea,” said Lillywhite.

The researchers captured 99 sea snakes off the coast of Costa Rica (interestingly, the snakes have never been observed in estuaries) and offered them freshwater in a laboratory environment. The team happened to be there just as six months of drought broke and the rainy season began. They found that only 13 percent of snakes captured after the rainfall began accepted the offer, compared to 80 percent of those captured before. The rainfall must have quenched their thirst.

The study continues many years of work by Lillywhite. The present paper was coauthored by Mark Sandfoss, Lillywhite’s current PhD student, Coleman Sheehy, his former student who is now the Collections Manager in Herpetology at the Florida Museum of Natural History, and then-Fulbright visiting scholar Jenna Crowe-Riddell.

“How these animals locate and harvest precipitation is important in view of the recent declines and extinctions of some species of sea snakes,” said Lillywhite. The question remains: How will climate change and its effects on precipitation impact the sea snakes?

UF professor receives NEH fellowship to research under-studied African writing traditions

Researcher: Fiona McLaughlin, 352-392-4829, fmcl@ufl.edu

Fiona McLaughlin, professor of linguistics and African languages at the University of Florida, has received a National Endowment for the Humanities Fellowship to work on a new book, Trans-Saharan Literacies: Writing across the Desert, in the 2019-2020 academic year. Only 8 percent of applicants were awarded fellowships this year. This fellowship will support McLaughlin in exploring the social consequences of two overlooked writing traditions in Africa.

The project brings a sociolinguistic perspective to two writing traditions used by populations within and adjacent to the Sahara desert to argue for the conceptualization of a trans-Saharan world of shared historical, religious, and linguistic influences. McLaughlin developed the project over the past decade as she and colleagues have identified cultural continuities across the Sahara. “I decided that looking at writing practices would contribute to reconceptualizing the Sahara and the areas directly to its north and south as a coherent cultural sphere of mutual influence rather than a barrier,” she says.

Both literature and popular conception have tended to portray the Sahara as a barrier between North Africa and sub-Saharan Africa, but McLaughlin’s work suggests that the Sahara should be conceptualized as a cultural sphere of influence, and of religious, economic and intellectual exchange, of which writing is a crucial part.

The research focuses on the everyday writing of African languages in scripts other than the Latin script, specifically the Arabic script, in a tradition known as ajami which arose in the 15th century, and tifinagh, which since the third century BCE has been used to write Berber languages such as Tashelhiyt in Morocco and Tamasheq in Mali and Niger. These vernacular literacies persisted throughout, and provided an important social function in resistance to the imposition of colonial languages. Despite their importance, these literacies have been under-studied, due in large part to colonial and postcolonial depictions of Africa as the “oral continent.”

“There are many ways in which colonialism and Western scholarship have constructed Africa, not least of which is painting it as a continent devoid of literacy before European intervention, and this is simply not accurate,” says McLaughlin.

Moreover, ajami and tifinagh are rarely counted in official surveys of literacy, meaning that we likely don’t have an accurate picture of the prevalence of written language in the region. McLaughlin’s research will break new ground by using these writing systems as a point of departure to re-conceptualize the three countries of the Maghreb (Morocco, Algeria, Tunisia), the West African Sahel (Senegal, Mali, Niger), and the Saharan country of Mauritania, as a coherent trans-Saharan sphere.

“Being awarded an NEH Fellowship allows me the precious gift of time off to concentrate on this project, and it also reaffirms to me that the project is an intellectually worthwhile one,” McLaughlin says.

At the center of almost every galaxy, there is a gigantic black hole, a massive marker of a star’s collapse into infinite density. Akin to the comparably infinitesimal cell, the black hole is the “nucleus” of the galaxy. When galaxies collide and merge, their black holes unleash ripples in the form of gravitational waves. The University of Florida has played a major role in the detection of these waves from smaller black holes; now, one of its astrophysicists, Laura Blecha, has helped study the galaxy mergers that produce their supermassive cousins.

In the largest-to-date survey of galactic nuclei in near-infrared light, using high-resolution images taken by NASA’s Hubble Space Telescope and the W. M. Keck Observatory in Hawaii, the researchers analyzed 96 galaxies from the Keck Observatory and 385 galaxies from the Hubble. The Hubble observations represent over 20 years’ worth of snapshots and 38 different observation programs from its vast archive. Blecha conducted simulations of galaxy mergers and compared them with the observations.

The images also provide a close-up preview of a phenomenon that must have been more common in the early universe, when galaxy mergers were more frequent. The team targeted galaxies with an average distance of 330 million light-years from Earth. Many of the galaxies are similar in size to the Milky Way and Andromeda galaxies.

The new study thus offers a preview of what will likely happen in our own cosmic backyard when our Milky Way combines with the neighboring Andromeda galaxy and their respective central black holes smash together. No need to worry; the process is several billion years away and takes a billion years itself. A galaxy merger creates a chaotic swirl of cosmic dust that can keep the circling dance of two black holes hidden from most telescopes.

Previous studies mostly captured colliding galaxies when their black holes were about 10 times further apart than those captured in this study. The clarity of observations in the present study is thanks to near-infrared instruments, such as at Keck Observatory, that can see through the dust. “X-ray observations are a great way to find dust-obscured black holes, so I wasn’t surprised that we found an association with galaxy mergers,” said Blecha. “But the number of close, merging galaxy nuclei we found was striking.”

The team first searched for visually obscured, active black holes by sifting through 10 years’ worth of X-ray data from the Burst Alert Telescope (BAT) aboard NASA’s Neil Gehrels Swift Telescope, a high-energy space observatory. “Gas falling onto the black holes emits X-rays, and the brightness of the X-rays tells you how quickly the black hole is growing,” explained Michael Koss of Eureka Scientific Inc., in Kirkland, Washington.

The researchers combed through the Hubble archive, identifying those merging galaxies they spotted in the X-ray data. They then used the Keck Observatory’s super-sharp, near-infrared vision to observe a larger sample of the X-ray-producing black holes not found in the Hubble archive.

To verify their results, Koss’s team compared the survey galaxies with 176 other galaxies from the Hubble archive that lack actively growing black holes. The comparison confirmed that the luminous cores found in the researchers’ census of dusty interacting galaxies are indeed a signature of rapidly growing black-hole pairs headed for a collision.

“Computer simulations of galaxy collisions show us that black holes grow fastest during the final stages of mergers, near the time when the black holes interact, and that’s what we have found in our survey,” said Blecha. “The fact that black holes grow faster and faster as mergers progress tells us galaxy encounters are really important for our understanding of how these objects got to be so monstrously big.”

The black holes grow at a fast clip as they engorge themselves with their cosmic food, and, being messy eaters, they cause the infalling gas to blaze brightly. “I looked at where the simulated mergers produced luminous, rapidly growing black holes compared to where we found them in the real mergers,” noted Blecha. In both cases, this speedy growth occurs during the last 10 million to 20 million years of the union. The Hubble and Keck Observatory images captured close-up views of this final stage, when the bulked-up black holes are only about 3,000 light-years apart — a near-embrace in cosmic terms.

When the two supermassive black holes in each of these systems finally come together in millions of years, their encounters will produce strong gravitational waves. Gravitational waves produced by the collision of two stellar-mass black holes have already been detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO), for which UF physicists developed the detection algorithm and the input optics for the interferometer. Observatories such as the planned NASA/ESA space-based Laser Interferometer Space Antenna (LISA) will be able to detect the longer-frequency gravitational waves from supermassive black hole mergers, which are at least a million times more massive than those detected by LIGO.

Future infrared telescopes, such as NASA’s planned James Webb Space Telescope and a new generation of giant ground-based telescopes, will provide an even better probe of dusty galaxy collisions by measuring the masses, growth rate, and dynamics of close black-hole pairs. The Webb telescope will also be able to look in mid-infrared light to uncover more galaxy interactions so encased in thick gas and dust that even near-infrared light cannot penetrate them. Adaptive optics systems in the next generation of very large-diameter ground-based telescopes that are being built will also study these galaxies at even higher resolutions (for example, the Thirty Meter Telescope, the European Extremely Large Telescope and the Giant Magellan Telescope).

The team’s results will appear online in the Nov. 7, 2018, issue of the journal Nature .

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

Divers avoid sharks for the obvious reasons — the teeth in their mouth — but the teeth in shark skin also have a bite. A mere bump can shred an expensive dry suit. Biologists, divers, and shark aficionados know about shark skin teeth, which are called dermal denticles, but little has been known about their development. Gareth Fraser, a biologist at the University of Florida, has been wondering about denticles for a long time and, in a paper published Nov. 7, 2018 in Science Advances, reveals surprising news about these toothy nubs. The paper was coauthored by his colleagues at the University of Sheffield, University of Oxford, and University College London.

Fraser, the corresponding author on the paper, has had a fascination with sharks since boyhood and “has been keen on shark tooth regeneration.” He says, “Why are sharks able to regenerate their teeth continuously through life? As an evolutionary biologist, I have been interested in the origins of teeth — teeth either came from the mouth or the skin.”

Some sharks regenerate their teeth every two weeks, and according to Fraser, a great white shark can generate as many as 50,000 teeth in its lifetime. However, dermal denticles do not regenerate like regular teeth. Curious to understand why, Fraser and his colleagues discovered that mouth teeth and skin teeth develop differently. “We already knew at least one gene expressed in mouth teeth is different from those in skin denticles, which led to the why and how you get these different structures that are otherwise the same in the skin and mouth,” says Fraser.

Prior knowledge of denticles was scant, and scientists thought that they developed randomly, with no pattern to them. “Every biostatistician and mathematician I talked to said, ‘There must be some sort of underlying pattern.’” This led the team to look at skin appendage development in different vertebrates.

Coauthor on the paper Rory Cooper then compared the development of denticles to feathers and discovered that shark denticles share a similarity with chick feathers. “We found these nice lines of gene expression in the skin that pattern where feathers eventually grow,” says Fraser. We thought maybe the shark does a similar thing, and we found two rows of denticles on the dorsal surface, which start the whole process — so shark skin teeth are precisely patterned during development.”

Even more surprising than the team discovering a true pattern to denticles, they realized that denicle development follows Alan Turing’s reaction-diffusion theory: equations that describe how molecular signals can interact to form complex patterns.

According to Fraser, shark skin teeth evolved for two reasons, the first being protection and the second being hydrodynamics. Denticles enable sharks to swim faster with less drag. Speedo, the swimsuit manufacturer, modeled its product, Fastskin, after a shark’s bumpy skin. The suit gave swimmers such an advantage that the LZR Racer suit was banned from the Olympics in 2009. Cooper says “Scientists and engineers have been trying to create shark skin–inspired materials to reduce drag and increase efficiency during locomotion. Our findings help us to understand how shark scales are patterned, which is essential for enabling their function in drag reduction.”

Fraser says the core genes that make and pattern all vertebrate skin appendages, from denticles to feathers and hair, share a common ancestry. In the course of his research with denticles, he came to a radical conclusion: Skin teeth likely evolved before oral teeth, and later their function shifted from protection to food acquisition. Fraser says, “The incredible thing is that not only are all skin appendages related genetically and evolutionarily, but the variation of type and arrangement we see in nature is controlled by fine-scale shifts in the Turing-like patterning mechanism.”

The research was funded by the Natural Environment Research Council and the Leverhulme Trust.

Read a rich-media version of this story.

Cojot movie posterThe University of Florida Center for Jewish Studies and the Jewish Council of North Central Florida will host a special rough-cut preview of Cojot, a feature-length documentary that follows the life of Michel Cojot-Goldberg, a Nazi hunter, Entebbe hostage, and ultimately, a Klaus Barbie trial witness.

Audiences will have a rare opportunity to provide input on a work-in-progress. The screening will take place at 7 pm on Thursday, November 15 at the Hippodrome Cinema.

Developed from a project at the UF Paris Research Center, and shot in numerous locations in France, UK, Israel and the US, Cojot is composed from hundreds of hours of footage, archival documents, and animation. The film includes interviews with Cojot family members, international Nazi hunters Beate and Serge Klarsfeld, and Operation Entebbe lead pilot Joshua Shani.

A riveting character study, Cojot is written, directed and produced by UF alum, journalist, and filmmaker Boaz Dvir (Jessie’s Dad, A Wing and a Prayer). Dvir is faculty in the Department of Journalism at Penn State University. The film is narrated by actor Judd Nelson (The Breakfast Club, St. Elmo’s Fire).

 

UF’s Dr. Gayle Zachmann, who serves as the feature-length documentary’s historical consultant and producer, will present the film. CLAS International Educator of the year (2016) and University Term Professor (2018-2021), she is Associate Professor in the Department of Languages, Literatures, and Cultures and the Center for Jewish Studies at the University of Florida.

Gayle Zachmann conducts an interview in Paris in 2015.

In recent months, Dvir and Zachmann have screened the rough-cut to more than 1,300 people around the country.

Director of the UF Center for Jewish Studies Jack Kugelmass, said “Projects like this come about because a faculty member is doing work on the ground, and there is no substitute for this. Sometimes these kinds of endeavors can really bear fruit. Here is a case where it has. The project has already had –and will continue to have—important implications for course development and student research projects as well.”

Zachmann, who developed the UF Certificate in European Jewish Studies, has been instrumental in curriculum building, regularly offering courses in French Jewish Studies at UF. Her research focuses on French Jewish writings and literary and visual cultures of the 19th and 20th centuries. She spent last summer in France and Israel interviewing for a class she is currently teaching on cultural flows between France and Israel. She notes: “Working on the film has been quite an adventure, from the very first interviews, to Boaz’s turn –much to my delight– to the story of Cojot. A perfect fit, and a wonderful opportunity for students–who were always part of the process–at both the University of Florida and Penn State.”

“We are excited to offer this special screening to the Gainesville community and delighted by the support we’ve seen over the years, on campus and off,” said Zachmann.

“I have seen this film emerge in its various stages and I am truly impressed by how it’s come together into a powerful and coherent whole,” said Professor Kugelmass, “I am particularly struck by the creative use of animation. This is something which might seem overly daring and difficult to integrate with footage […], but Dvir succeeds and it makes the film that much more compelling and a pleasure to watch.” He added, “This project has been an excellent one for the Center and UF. It has given students hands on experience in filmmaking, editing, translation, and wonderful outreach to the community. It presents a new and exciting way for academics to present their work to the larger community.”

Dvir’s previous film, the PBS documentary A Wing and a Prayer, has screened around the world and won Best Feature Documentary at the 2016 Fort Lauderdale International Film Festival. The Guardian’s Hadley Freeman wrote: “It wasn’t until I saw Boaz Dvir’s very moving forthcoming documentary about him, Cojot, that I truly understood Michel’s life, and perhaps the message of it.” Cojot is a co-production with Matthew Einstein and Richie Sherman.
This special fall sneak preview will also include trailers for the Ninth Annual Gainesville Jewish Film Festival, which will run from Sunday, March 17 through the 30th. Admission is $10. Students are admitted free with valid ID. Tickets may be reserved now. For more information about the screening or for assistance with reserving and purchasing tickets, please contact the Jewish Council office at 352.371.3846.

Sneak preview event hosted by the Gainesville Jewish Film Festival and co-sponsored by the UF Center for Jewish Studies, the Jewish Council of North Central Florida, the UF Harry Rich Endowment for Holocaust Studies, and Hadassah of Gainesville.

Read the note about Cojot in Ytori.

Ecological theory holds that plant-hungry creatures help shape ecosystems by mowing down dominant plants that might smother other plants, thus enhancing biodiversity — but only if the area is lush. A new study co-authored by University of Florida biologist Todd Palmer in today’s edition of Nature Ecology & Evolution shows that this widely-believed theory might not be entirely true.

The researchers synthesized data from more than 250 vegetation-heavy areas, examining areas both grazed and non-grazed by large herbivores. “Large herbivore populations are in decline in ecosystems across the globe, and so understanding how these declines are likely to affect biodiversity is really important,” said Palmer. This paper takes some important steps in clarifying where and when we might expect these declines to have big consequences for the surrounding ecological communities.

By comparing data on the effects of herbivores on plant communities across a wide range of productivity, the researchers found that the effects of grazing animals on biodiversity could be predicted by understanding the impact that herbivory has on plant dominance. When grazing animals reduced dominance by feeding on abundant species that appealed to their tastes, the grazers increased biodiversity by freeing up resources for other, less dominant plant species. However, in areas where the most abundant plant species are resistant to grazing, herbivores increased dominance by feeding on the rare and tasty species, thereby reducing biodiversity.

“There’s been a lot of confusion out there in the literature trying to understand why herbivores sometimes increase and sometimes decrease biodiversity, and this paper really nails why they have different effects under different circumstances,” said Palmer.

These results suggest that management of dominance, not of grazing activity per se, is key to conserving biodiversity.