the us says it agrees with britain that russia was behind the nerve agent attack that poisoned a former spy and his daughter on uk soil. moscow's ambassador to the un denied russian involvement in the attack. earlier, britain announced the expulsion of 23 russian diplomats. tens of thousands of students have walked out of classrooms across the united states to call for tighter gun controls. they staged a 17—minute protest to represent the 17 people who were killed in the florida school shooting exactly a month ago. researchers in the united states say they have found particles of plastic in some of the most popular brands of bottled water. in the largest study of its kind, more than 200 bottles were screened. an average of ten plastic particles per litre were discovered, each larger than the width of a human hair. now on bbc news, click. this week: the app that helps record

and report sexual assault. the ai going after cancer. and the man who wants us all to live forever. as international women's day was marked this week, it brought with it further focus on the many issues still to be faced in bringing about true gender equality in all walks of life. the technology industry, of course, has its own issues, as we'll hear later. silicon valley's culture and its treatment of women raises a lot of questions. but tech can also be a force for good. it's beenjust six months or so since the me too movement gave

a voice to so many women around the world, who used social media to expose just how widespread sexual harassment and assault is. many women feel that reporting sexual assault can also be really traumatic, and the experiences of some women in silicon valley have spurred them to create something that may make thatjust a little bit easier. sumi das has travelled to stanford university to meet survivors of sexual abuse, and the creators of callisto. every tattoo tells a story. for stanford university studentjacqueline lin, the story is bittersweet. lin was one of 50 sexual assault survivors invited to share the stage with lady gaga during the 2016 oscars. while we were rehearsing, i remember at one point we were all crying and hugging each other, and someone just said, "we need to get a tattoo to commemorate this and to give us strength."

something to look at when you are feeling down, and you know that you're alone. lin says that a few days after she was assaulted by a friend in 2015, she told the title ix office, which investigate sexual misconduct. i decided to report because i didn't want him to do it to anyone else, and later i did find out that he had done a lot of... a lot of harassment, stalking and also assault on someone else. what was that experience like? it was awful. my gpa dropped down, and i was fighting with the school back and forth every single hour, every single day. lin, now an activist, wants greater transparency in the adjudication process. they're trying to cover up the number of sexual assault that happen on their campus, because that makes your university look safer. it's better for your public relations. stanford told click: stanford changed its title

ix process in 2016 and has begun reporting case numbers. in the us, one in five women is sexually assaulted while in college. i was sexually assaulted by a friend. over a year after that happened, i decided to report my assault, and i ended up finding the process of reporting to be more traumatic than the event itself. feeling not believed by the people who i thought were there to protect me was incredibly destabilising. jessica ladd's ordeal spurred her to create callisto, so survivors would have a way of reporting sexual assault. they can, one, just say what happened to them with a timestamp, doesn't have to go anywhere if they don't want to. two, report electronically to the authorities at their school. or three, just say what happened to them for now but report electronically if someone else names

the same assailant. you can think of callisto as an international information escrow agency. it holds onto records and only alerts schools when there's a match. students often report to protect others. this matching feature helps do that by detecting repeat offenders. people might use different names, they may look different. how do you make sure you've got the right person? we ask victims to put in notjust the name of their perpetrator, but also a series of unique identifiers. currently, facebook profiles are used to match. some students want more ways to id, and callisto may add mobile numbers and e—mail addresses in the future. 12 us colleges use callisto. the university of san francisco was the first. we knew students weren't reporting. if you look at our numbers from once we first started with callisto, three years ago, to now, there is definitely an increase in reporting. callisto allows for our students to write what happened, to write about the incident. and sometimes just writing your perpetrator‘s name

gives people power. seeing the need for callisto, shanta katipamula led an effort to bring it to stanford. it is just available 21w, and they have seen spikes in usage during times like spring break, when the title nine office might not be available, but students wanted to file a report, or during the weekend, when no—one‘s staffing. with callisto, survivors recount what happened at the own pace, privately. often victims, including in in—person interviews, will want to seem credible, so they want to fill in all the details and tell a wonderful story arc. but that's not how memory works, and that's particularly not how memory works in the event of trauma. so being able to allow somebody to say i don't know the centre, i am not sure that, and only record think that they are sure of, is really essential to make sure that that time stamped record isn't later used against them. students must create a username, password and pass phrase that can't be recovered.

not quite a one—click sign up. that deters some users. for callisto, it ensures privacy. because then we'd have to be storing the password, which means that we could potentially decrypt the data, and we want to make sure that even we can't view what's in the form. since students choose whether to report assaults, some records are never seen by schools. but they're still useful. we provide our institutions with at an aggregate data report that gives them a better sense of what is happening in that store record, what type of years are assault occuring, what type of assault is it? is it involving alcohol, is it not? what class years are involved? others are also working to make reporting less daunting. the spot app creates a record from the user's conversation with a chat bot, while all voices will let them report electronically. lin isn't sure electronic reporting would have changed her was handled, but she see the potential. what i think callisto is great for is to track perpetrators.

if they decide to apply for grad school or transfer schools, i think that's where this can really come in and have a very powerful effect. as we grow, we want to create one system, one database that allows us to track any perpetrator, even as they move through space and time. which would give survivors a way to find out if their assailant is a repeat offender, something ladd says she wonders to this day. that was sumi das at stanford university. now, while callisto was created a team of mostly women, that is rare. even right here in silicon valley. whenever i've been to visit, i've found it all too easy to think of the valley as sharing the progressive values of san francisco, where all colours and genders seem welcome. but the people i have met,

those in charge of the start—ups and tech giants, have been mainly men. it is quite obvious to us that women are underrepresented here, and there are those who feel that silicon valley is just as full of sexism and masculine culture as anywhere else. it's the social challenge where the majority of people... emily chang is a san francisco journalist, and the host of bloomberg technology. and in her new book, brotopia, she's written about the industry that has always self—selected for men. first came the antisocial nerd who suddenly became part of the ruling class, and now she says it's the time of the cocky, self—confident risk taker, the bro. silicon valley is the heart of the most powerful industry in the world, and that is the technology industry. this is a world that is controlling what we see, what we read, how we shop, how we communicate, how we get around. the reality is, the exclusion from this incredible and progressive industry was not inevitable.

it didn't have to be this way. i think of all the women out there who might have started the next facebook or the next google or the next apple, but never got the chance because they didn't look the part. and that is something that needs to change. women hold just 25% ofjobs across the computing industry. they account for 7% of investors. women—led companies getjust 2% of venture capital funding. the most important thing that we need to do is to acknowledge that silicon valley has become toxic for women. so what is bro culture? well, it is exactly what it sounds like. fratty parties, beer, behaviour that is alienating towards women. i had 12 women overfor dinner at my home, most them engineers who work at companies like uber and google, and the uber engineers told me specifically they would often be invited to strip clubs and bondage clubs in the middle of the day, there was a heavy drinking culture. and so much of the work in silicon valley gets done

outside of the office, so at the bar, at the conference, in a hotel lobby, and they're stuck in sort of an impossible catch—22. if they attend, they're disrespected and discredited. if they don't, they're shut out of important business and networking opportunities, because very powerful people, very powerful men, are at these parties. so many female entrepreneurs that i've spoken to have notjust one story, but several stories to tell about how an investor has crossed a line. you know, one of the most sort of egregious examples that i have found is an investor who... a very prominent investor in companies like twitter and uber who often hosted hot tub parties at his home. well, what female driven wants to get in a hot tub and future business while wearing a bikini and drinking beer? these are the kinds of activities that have been very alienating to women, and unfortunately have created a very unlevel playing field

in silicon valley. i think about how different the world might be if women had been at the creation of some of these companies from the start. i sat down with twitter co—founder ed williams, and i asked him, if women had been involved in the founding of twitter, would online harassment and trolling be such a problem? and he said he doesn't think so. they weren't thinking about that when they were building twitter. they were thinking about all the wonderful and amazing things that can be done with twitter, they weren't thinking about how it can be used to send death threats or rape threats. and as a result, online harassment is one of the biggest problems plaguing internet today. if women had been more involved in building these products and building these services, maybe online harassment and trolling wouldn't be such a problem. i fully believe that the people who have already changed the world in so many wondrous ways, the people who are taking us to mars, the people who are building self—driving cars, the people

who have given us rides at the push of a button, if they can do all that, they can change this too. hello, and welcome to the week in tech. it was the week that sony blocked the videogame super seducer for being released on the playstation 4. it's been criticised as too sleazy and for promoting toxic behaviour. dyson announced it won't be making plug—in vacuum cleaners any more, they'll be developing their cordless battery range. dating app bumble has banned members from posing with guns in their profile pictures, though an exception is being made for military and law enforcement officers in uniform. solving in three, two, one. and a robot managed to solve a rubik's cube in under a second. blink and you'll miss it.