To provide communications, programs, services, and activities of interest to TI and former TIers around the world.

Around TI

Subscribe to Around TI feed
The company blog of Texas Instruments.
Updated: 14 min 34 sec ago

Updated robotics kit brings technology to life for university students

Tue, 09/24/2019 - 3:30am

A summer intern at our company with her TI-RSLK MAX.

The summer internship was nearing its end and the robotics competition was approaching fast. That’s when Aaron Barrera realized that the closet doors in his apartment – off their hinges and leaning against a wall – would make a great practice maze to prepare for the competition.

So Aaron and three electrical engineering classmates from the University of Florida – all summer interns at our company – laid the doors on the floor, rolled some strips of black electrical tape into a maze, assembled the TI-RSLK MAX in less than 15 minutes and began pushing the robotics system to its limits.

Aaron Barrera (center) and other members of the team programmed their TI-RSLK MAX before the intern competition this summer.

They wanted bragging rights from doing well in the competition, of course, but also understood how the robot could help them become better engineers as they looked ahead to graduation.

“You can propel yourself as an engineer, learn something in the process, and set yourself apart as somebody who likes to solve problems and innovate,” said Sebastian Betancur, a member of the team.

Bringing technology to life

The TI Robotics System Learning Kit family – with the TI-RSLK MAX being its newest addition – is a low-cost robotics kit and curriculum for the university classroom that is simple to build, code and test with solderless assembly. The system can solve a maze, follow lines and avoid obstacles. Students can use the curriculum to learn how to integrate hardware and software knowledge to build and test a system.

Learn more about the TI-RSLK MAX

The system uses our SimpleLink™ MSP432P401R microcontroller (MCU) LaunchPad™ Development Kit, easy-to-use sensors and a chassis board that transforms the robot into a learning experience. Students can use wireless communication and Internet of Things (IoT) capabilities to control the robot remotely or enable robots to communicate with each other.

“From an academic standpoint, the topics are rich – from circuits and software to interfacing and systems and the Internet of Things,” said Jon Valvano, the University of Texas at Austin electrical and computer engineering professor who collaborated with our team to develop the TI-RSLK family. “And it’s done in a way that is fun and understandable by students. The TI-RSLK is educationally powerful.”

And its benefits extend beyond the classroom.

“In the future, students will have to self-learn and adapt,” said Ayesha Mayhugh, a university product manager at our company. “We don’t know how our jobs are going to change in the future. Having the ability to bring these complex concepts to life and be a self-learner, beyond what is taught in classrooms, will be critical for success.”

Jon Valvano, a University of Texas at Austin professor, collaborated with our team to develop the TI-RSLK family of educational robots.

Learning platform

The University of Florida team spent some long, pizza-fueled weekends in Aaron’s Dallas apartment – interrupted with occasional video games – to program their robot and prepare for the intern competition in late July. Competitors were judged on the speed their robots navigated the maze, the amount of power they used and innovation. The team from Florida didn’t win, but they did appreciate the new robot and the support behind it.

“It’s a really good learning platform,” said Daniel Bermudez, also a member of the team from the University of Florida. “People who work with this can see how an embedded processor can be used for fun and learning.”

“It is very well made,” team member Colin Adema said. “The documentation, the code and other support helped a lot. We could have been metaphorically and literally spinning our wheels without that support, but being able to just start it up and start implementing our own code and algorithms pushed us to keep working.”


From concept to cosmos: How Jack Kilby's integrated circuit transformed the electronics industry

Tue, 09/17/2019 - 10:00am

In 1958, as one of the few employees working through summer vacation at our company, electrical engineer Jack Kilby had the lab to himself. And it was during those two solitary weeks that he hit upon an insight that would transform the electronics industry.

Since 1948, transistors had begun to replace large, power-hungry vacuum tubes in electronics manufacturing, but hand-soldering thousands of these individual components onto a chip was expensive, time-consuming and unreliable.

Jack’s insight was that the same semiconductor materials used to make transistors could be tweaked to produce resistors and capacitors, too. This meant an entire circuit could be produced from a single slice of semiconductor material.

Later that year, on Sept. 12, Kilby presented his invention: An electronic oscillator formed from a small slice of the semiconductor material germanium. The first integrated circuit was born, bringing with it the exponential growth of the electronics industry and the spread of electronic devices throughout every aspect of our lives.


Learn how Jack Kilby’s integrated circuit and our people helped land man on the moon 50 years ago.

Unleashing creativity in electronics

Our company needed a showcase device, something that could prove the integrated circuit's potential to take large, unwieldy and expensive technology out of specialized computing labs and into the wider public's offices, homes and pockets. They settled on a hand-held calculator.

At the time, a calculator was a large desktop machine that required a constant AC power supply. When our prototype was unveiled in 1967, it used just four integrated circuits to perform addition, subtraction, multiplication and division. It weighed 45 ounces and could fit in the palm of your hand.

Chip complexity began to grow exponentially, now that the creative energy of electronics engineers was finally unleashed from the constraints of wiring together individual transistors. The most significant result was the creation of the first microprocessor, which packed the workings of an entire central processing unit into less than a square inch – and supported the development of the first portable computers.

Circuits in space

The miniaturization of electronics came in handy for coordination of the first moon mission, since the idea of launching the car-sized mainframes used by NASA's ground control up on a rocket itself was both physically and economically impossible.

Instead, the space agency created the world's first integrated circuit-based spaceflight control system, the Apollo Guidance Computer. In July 1969, running around 145,000 lines of code with 12,300 transistors, this 70-pound computer successfully coordinated both Neil Armstrong and Buzz Aldrin's arrival on the moon – and their safe return to Earth eight days later.

Ubiquitous Computation

Chips many thousands of times more powerful than those used in the Apollo Guidance system can now be found everywhere from factory robots to car dashboards, cell phones, computers, smart watches and smart speakers. They can even be found inside the ears of millions of people around the world in the form of hearing aids.

Forty-two years after that pivotal couple of weeks in 1958, Jack accepted half of the Nobel Prize in physics for his invention. In his acceptance speech, he reflected on the host of electronics innovations that have been developed since – far beyond what he’d imagined possible at the time: "It's like the beaver told the rabbit as they stared at the Hoover Dam. 'No, I didn't build it myself, but it's based on an idea of mine.'"

There’s more than one right answer in Jacob Day’s engineering class

Tue, 08/20/2019 - 9:48am

Jacob Day smiled down at an empty table in the engineering classroom at Wylie East High School. Two years ago, he would have been readying the space for the students’ first day, setting out nuts and bolts, pieces of aluminum, motors, wires and other building materials.

“When it was my classroom, this would have been covered in pieces of metal,” he said, waving a hand over the empty table and laughing at the memory. “My classroom was a mess.”

The mess was a hands-on makerspace: a place to tinker, experiment and collaborate. A place to struggle through failure and learn to improve. A haven for high school students who wanted to learn the basics of engineering – all through a program built by Jacob from the ground up.

He took a five-year break from his career as an analog design engineer at our company to teach students that the best way to learn engineering is through trial and error. He assigned them projects with minimal directions or information, challenging them to find a way to build things like a water-powered bottle rocket, a bridge built of toothpicks or a removable door-window blind.

“The educational system tends to teach kids to solve problems based on a recipe that leads to a single, correct solution," he said. “But the real world isn't like that. There’s more than one right answer.”

At first, the students hated not being told how to do things.

“But eventually the light would come on," he said.

Learn more about our commitment to education.

‘A fantastic way to learn’

Emily Esch was a new eleventh-grader at Wylie East in 2013 when she spotted a flier about a robotics club. Though she had no technical background—she was focused on art—Emily checked out the club on a whim.

Jacob, the teacher who put out the flier and who was also new to the school, welcomed her warmly. He even convinced her to use her free period to attend an engineering class he had also just started.

“I was nervous at first, but the more I learned from Dr. Day, the more confident I became," she said. By her senior year, she became the robotic club’s president.

"It ended up being a life-changing experience,” said Emily, who is an information technology major with a special interest in data analytics at the University of Texas at Dallas. She’ll graduate this May.
Jaxson Hill also thought Jacob’s class was life-changing. A top student, Jaxson was initially frustrated by Jacob’s course, bumbling through efforts at solutions that inevitably fell short.

“We'd fail, and we'd have to scrap our approach and try again," Jaxson said. “But Dr. Day would slide around the room in a rolling chair from team to team, answering our questions and giving us pointers. We'd end up learning from the failure and figuring out what worked.”

He took three classes with Jacob before graduating. He’ll be starting at Harvard University this fall, where he intends to major in mechanical engineering.

“It was a fantastic way to learn," he said.

A connection meant to be

Jacob has always felt a connection to teaching. Both his parents had been life-long teachers, and he helped pay his way through college by tutoring in the math lab.

“I seemed to have a knack for explaining technical things in ways people could understand," he said. “I thought I might try teaching after I retired."

Jacob Day at a robotics competition with Wylie East student Abigail Ritter

But in 2013, Jacob had a conversation with a Wylie school district administrator who had been thinking of hiring a teacher to start an engineering course. “It felt like more than a coincidence to me," said Jacob, who lives in the North Texas community with his wife and four young children. “I think it was meant to be."

He started with about 40 students as the first and only engineering teacher at the school – but word spread about his class, and soon more teachers were needed. Candice Lawrence, who until then had been a junior-high-school science teacher, was asked to help.

“Jacob taught me about engineering from the ground up, and I'd help him come up with the lesson plans,” she said. “I was especially afraid of having to teach robotics, but he promised me I'd love it. He was right."

Last year, the engineering program grew to 500 students and five teachers. That's when Jacob knew the program was sustainable. He felt he could return to his passion working in the field as an engineer at our company.

But he remains involved in Wylie schools: He ran for a seat on the school board last fall and won.

“I think about those selfless teachers who are there for the kids every day," he said. “I felt there should be someone on the board who could speak on their behalf."

He also keeps his hand in the now-substantial engineering and robotics activities in the school district. He's helped extend the engineering program down to the junior high school and continues to serve as a mentor for the robotics program, which now boasts three teams and several entries into state competitions.

“I feared we were losing him when he said he was leaving," Candice said. “But he's remained very involved with the students. Whenever we need him, he comes."

How education is opening doors in Bangalore

Tue, 08/13/2019 - 5:50am

Kiran as grown up in a single small room that does not have running water. But he has a goal: He wants to be an engineer. “Engineers come up with all the ideas,” he said. “They’re the ones who innovate.”

Kiran has grown up in a small room that he shares with his parents and two younger sisters. The room has one light bulb, no running water and no restroom.

Despite his humble circumstances, Kiran was the top student in the government elementary school that serves his community. He now attends a selective Bangalore-area boarding school where he’s studying in English and is being exposed to sports, music and even yoga classes. And the 12-year-old has set a tough, but rewarding, goal.

“I want to be an engineer,” he said through an interpreter. “Engineers come up with all the ideas. They’re the ones who innovate.”

Kiran, 12, was the best student in his elementary school and now is attending a selective boarding school near Bangalore.

Opening the doors of opportunity

While government schools are accessible to children from low-income households like his, there is a need for better amenities, infrastructure and teaching support to encourage more children to attend school. And today – thanks to a partnership between our company, non-governmental organizations and some of the government schools – Kiran and other motivated students are embracing education as the path out of poverty and into a better future.

We believe every student is capable of changing the world and engineering their future.
Learn more about our commitment to improving education.

The help begins with the basics: providing back-to-school backpacks and notebooks, installing clean drinking water systems, offering breakfast and lunch, building separate restrooms for boys and girls, organizing health checkups, painting the school, and paying the salaries of some teachers so that schools are adequately staffed for learning.

Our company provides computer labs and pays the salaries of the computer and English teachers in the elementary school that Kiran attended.

“If a child does not have food to eat, clean water to drink or access to a basic education, we have to focus on that before we can help them learn topics like science, technology, engineering and math,” said Aditya Salian, who manages our company’s corporate citizenship efforts in India.

This year, our company will provide back-to-school resources for about 18,000 students in 130 schools in Bangalore and in far-away rural areas.

After the basics are in place, the doors of educational opportunity swing open. Our company has adopted 16 schools where we provide in-depth support to about 2,000 students, including computer labs, science labs, backup power supplies, visits to historical sites, smart classrooms and learning centers where students can get help with their homework – all far beyond what’s typically available in public schools. We also fund mobile science centers – many sent in vans or even in boxes on the backs of motorcycles – that serve about 120 schools in rural areas.

Passion for volunteering

Ganesh Shamnur, a design automation manager for our company, is among the hundreds of TI volunteers who spend much of their free time improving educational opportunities for students in India. Every year, like many TIers, he loads up boxes of backpacks and notebooks and sets off by train on a couple of 12- to 14-hour journeys to villages in some of the remotest, hardest-to-reach areas of southern and western India. His mission: Work with local non-governmental organizations to deliver the school supplies, check on learning centers we support and, just as important, let the students know that someone cares.

“Many of the kids don’t even have proper shoes,” he said. “In these situations, a school bag or a notebook and pen are luxuries and amazing motivations for students to be in class.”

Aditya Salian manages corporate citizenship initiatives for our company in India.

That passion for volunteering is an important part of our support for education.

“Volunteering is integral to our whole program,” Aditya said. “Volunteers are driving it, and that makes a difference in the communities. The people know we’re not just throwing money at problems. We’re getting involved.”

But the volunteers get something in return.

“I started volunteering because I saw my parents help many people when I was growing up,” Ganesh said. “But it has become a habit and then I started enjoying it. It’s an amazing feeling to see people get pleasure with the help we provide.”

Changing mindsets

Getting parents to send their children to school isn’t easy in the low-income communities in Bangalore. While government schools are accessible to most of the population, they often aren’t equipped with the facilities, teachers and other support to provide the education that children need. The government system provides one teacher for every 30 students, and the teachers have to go door-to-door to recruit students.

The first year that Pavithra was headmistress at Kiran’s school, 2005, the school had 12 students who met in a single small room and didn’t even have paper or pens. But with clean new restrooms, pure drinking water, back-to-school supplies and uniforms, computer and English classes, and other educational opportunities that our company has provided, attendance has increased to 78 students.

Pavithra is the headmistress of Kiran’s elementary school. She goes door-to-door to recruit students for her school.

“Most of the parents here are daily wage workers,” Pavithra said. “For them, even the expense of notebooks and bags is big. They’re not comfortable spending the money. But because of TI, we don’t have that problem here. We are able to provide the basic things they need, including uniforms.

“To clap, you need two hands,” she said. “While teachers, parents and support staff are one hand, the support we get from TI is the other hand. Both are required to clap. I hope the sound and energy of the clapping is in the lives of the children.”

And now Pavithra is persuading parents of the best students to send their children to a free boarding school after fifth grade. The first year, only one student attended the school. This year, the second for Kiran’s school, five have been admitted.

“Most of the parents here haven’t been to school, so these students are first-generation learners,” she said. “Most of the parents are daily-wage workers and many of the students only aspire to that kind of life. They don’t have examples in their day-to-day lives about how education can bring about change. So this is a huge change in the mindset of the parents. They are OK sending their kids for a better future.”

Kiran’s parents are convinced about the importance of learning and committed to his education.

“I do not have any hope of wealth,” Kiran’s father, Shyam, said through an interpreter. “Whatever I earn, I’m putting into my children’s development. I hope they’ll get educated and have a better future.”

Celebrating 50 years: One giant leap for TI’s integrated circuits

Mon, 07/15/2019 - 1:30pm

TI aerospace engineer Verie Lima and his family were swimming in a neighborhood pool in the Dallas area on July 20, 1969, when he suddenly heard a woman’s voice shouting, “It’s about to happen!”

“Man was about to land on the moon,” Verie said. “Everybody jumped out of the pool at the same time and got in their cars.”

Within minutes, Verie and his wife and three kids were home, watching the historic moon landing on the television in their living room.

“The biggest thought I had was about the technology that was letting that happen,” said Verie, who retired from our company.

It was a surreal moment – the culmination of years of work for engineers like Verie, who was a TI circuit designer for the unmanned space program. TIers developed products that were used in Apollo 11 systems to steer the lunar excursion module, to initiate and terminate rocket bursts, and control radar and navigation gear essential to the success of the moon landing.

Verie was captivated as he watched Neil Armstrong’s first steps on the moon. But he was also thinking about work.

“It was really important to me that Apollo 11 was a success, because if it failed, the failure would have propagated to other areas of the space program,” he said. “The moon landing meant that I could continue my work.”

Fifty years after our company’s people and products helped land man on the moon, we are still innovating technology for space exploration. Learn more. 

A front-row seat to the space race

In the 1960s and ‘70s, Verie worked on ICs that went into the Mariner and Voyager spacecrafts. He and thousands of other TI employees had a front-row seat to the space race.

Sid Parker, a TI chemist who retired from our company, developed a process to create mercury cadmium telluride material that was used to enable forward-looking infrared (FLIR) cameras that sense infrared radiation.

“Forward-looking infrared creates images with very nice details and has many uses, including seeing out into the depths of space,” Sid said.

Solving technical challenges to enable space exploration was critical to fulfilling President John F. Kennedy’s goal to put man on the moon within the 1960s.

“Kennedy said before he died that landing on the moon would happen within the decade, and we believed we could be leaders in developing the technologies to make it possible,” Verie said.

Russia had succeeded in photographing the far side of the moon in the late 1950s, and was ahead in the space race before Apollo 11.

“We were trying to keep up with Russia, but we couldn’t,” Verie said. “We were behind. And the Russians really owned the activity on the moon.”

Many of the ICs Verie designed decades ago are still in space today. Voyager II, for instance, has not retired from flight. Using technology from the 1970s, the spacecraft continues to explore planets and has reached more than 13 billion miles from Earth. Its photographs have answered some of the mysteries of the universe – like whether there is life on Mars – all on about the same amount of electricity that it takes to power three lightbulbs, Verie said.

“Voyager was kind of our program equivalent to going to the moon because it did something that no one else had ever done and still has never done – it achieved more than 40 years of space exploration,” Verie said.

Solving the technical challenges of space flight

Voyager, Apollo, Mariner – these space missions may never have been possible without the invention of the IC. Eleven years before man’s historic first step on the moon, engineer Jack Kilby handcrafted the first IC in a lab at our company. Though it wasn’t immediately recognized, the IC would help solve technological challenges of space flight because it allowed engineers to put multiple electronic circuits on a small, flat piece of semiconductor material, saving weight and power.

“The less weight you have and the less power you use and the less volume you take, the more experiments you can put on the spacecraft,” Verie said.

The IC had to undergo tremendous advancement between Sept. 12, 1958, when Jack first unveiled the technology, and July 20, 1969, when Neil Armstrong took that first small step.

“The problems were not circuits or components as much as the technology to do it right in a zero-gravity environment,” Verie said.

“It took only 11 years after coming up with a brand new idea as innovative as the first integrated circuit to using it in the most critical mission in the history of aerospace, and that was Apollo 11. And it happened at TI,” said Chief Technology Officer Ahmad Bahai.

Driving the cost down

In 1959, the Air Force funded a project at TI to research manufacturing processes for the IC. The resulting pilot project helped drive down the cost of the IC from $1,000 apiece to $450*, and manufacturing advancements over the next few years drove the cost per chip down much further, to $25.

In 1962, engineers at our company designed the first IC equipment ever to fly on a rocket into space**.  It was used to create a counter to study the radiation trapped in the earth’s magnetic field***.
In 1964, our engineers built the command detector/ decoder for the Ranger 7. The space probe successfully delivered the first close-distance imagery of the lunar surface, allowing scientists and engineers to determine the safest landing area for the Apollo astronauts***.  

Today, ICs remain the cornerstone of modern electronics, and their capacity, power efficiency, size and speed has increased exponentially. In fact, the IC enables whatever smart device you may be holding right now and many other things you touch every day. A modern IC may have billions of transistors on a surface smaller than a dime.

“Your smartphone has 240,000 times more memory and is 100,000 times faster than the components on the Voyager spacecraft,” Verie said. “Imagine that.”

As for the future of technology, Verie thinks it’s beyond our imagining.

“If you stand where we came from when Jack Kilby invented the first integrated circuit in a TI lab in 1958, we’ve come a long way. I wouldn’t rule much of anything out.”

To learn more about the journey of the IC from invention to today, check out our blog post on Sept. 12, 2019 – a day we at TI call Jack Kilby Day.

* Engineering the World by Caleb Pirtle III, pg. 85-86
** Engineering the World by Caleb Pirtle III, pg. 39
*** Engineering the World by Caleb Pirtle III, pg. 39
**** Engineering the World by Caleb Pirtle III, pg. 39

New metering technology makes every drop count

Tue, 06/25/2019 - 8:16am

The statistics are alarming: In the United States alone, household leaks waste about 900 billion gallons of water each year. To put that number in perspective, that’s enough water to supply about 11 million homes annually.1 And other countries – from Europe to Asia – face similar challenges. Compounding this problem are anticipated water shortages.2

But help is here. Ultrasonic technology gives water meters installed in smart buildings and smart cities the ability to detect and localize leaks as small as one drop every few seconds. Cities from Austin to Antwerp are installing high-tech smart water meters that give customers the information they need to find leaks and conserve water while helping utilities identify infrastructure leaks in aging pipes and broken water mains.

“The water we have today is the only water we will ever have,” says Holly Holt-Torres, water conservation manager for the City of Dallas Water Utilities. “We have to conserve it. Technology will allow us to do that at an increasingly higher level.”

But this ultrasonic technology has applications that extend beyond water meters. The same technology can be used in meters that measure natural gas flow and even detect the mixture of gas flowing through pipes. It can even help medical professionals regulate oxygen delivery in surgical equipment.


Learn more about our ultrasonic sensing MSP430™ microcontrollers.

Going with the flow

Ultrasonic waves, of course, are not new. Bats, for example, use ultrasonic ranging to avoid obstacles and catch insects at night. And in more high-tech applications, it is used in material discernment, collision avoidance in automobiles, and industrial and medical imaging.

Now it’s being used in water meters and other flow meters. Meters traditionally have relied on an electromechanical system with a turning spindle or gear that uses a magnetic element to generate pulses. But – as is the case with thermostats, motors and lots of other everyday devices – electromechanical systems in flow meters are rapidly transitioning to electronic systems.

In these systems, a pair of immersive ultrasonic transducers measures the velocity of acoustic waves in the fluid. The velocity of acoustic wave propagation is a function of the viscosity, flow rate and direction of the fluid flowing through the pipe. Ultrasonic waves travel at different speeds depending on the stiffness of the media they’re traveling through.

The accuracy of the measurement depends on the quality of the transducer, precision analog circuitry and signal processing algorithms. Acoustic or ultrasonic transducers are piezo materials that convert electric signals to mechanical vibrations at a relatively high frequency of hundreds of kilohertz. Typically, a pair of ultrasonic transducers in the range of 1-2 MHz must be well-matched and calibrated in order to measure flow accurately. They make up a significant part of the flow meter’s cost. The sensor system must operate at very low power to ensure a 15-20 year battery life.

Our company’s advanced flow metering chip, the MSP430FR6043, includes a unique analog front end and algorithm, which significantly improves accuracy while reducing overall cost and power consumption. Our flow metering architecture leverages high-performance analog design, advanced algorithms and embedded processing to mitigate the need for an expensive pair of ultrasonic transducers. Analog front end and signal processing algorithms compensate for transducer mismatch.

Making every drop count

A typical ultrasonic flow meter transmits an ultrasonic wave and measures the differential delay at the receiver to estimate the rate of the flow. Delay measurements are usually handled by a time-to-digital-converter circuit that monitors the zero crossing of the received waveform. The challenge with the typical approach is that it is not sensitive enough to detect flow levels with high accuracy.

Our architecture deploys a smart analog front end featuring a high-performance analog-to-digital converter to improve signal-to-noise quality and overcome calibration inaccuracies. This approach has several benefits:  

  • It can achieve higher accuracy by reducing interference and improving signal-to-noise ratio.
  • The architecture can measure a wide dynamic range of flow, from a fire hose to a small leak.
  • By using a lower voltage driver, it significantly saves on power and cost. The average current for one measurement per second is less than 3 microamps. This translates to a battery life of more than 15 years.
  • It can detect turbulence, bubbles and other flow anomalies, which is important for flow analysis and servicing the pipelines.
  • The technology is robust to amplitude variations in the two directions of the flow, which may occur in water and gas at higher flow rates.

Many other TI technologies are critical for a high-performance flow meter. A low-power microcontroller with integrated ultrasonic analog front end, a high-performance clock reference, a low-quiescent current power management and ultra-accurate impedance matching of transmit driver and receive amplifier paths are examples of additional differentiating technologies in these flow meters.

Together, these technologies can help conserve one of our most precious resources.

Learn more about our ultrasonic sensing solution library for ultra-low-power flow metering devices.

Read our Corporate Citizenship Report to learn how our company is committed to conserving water and other resources.

1 Environmental Protection Agency

2 Earth’s Future: Adaptation to Future Water Shortages in the United States Caused by Population Growth and Climate Change.