Humans can observe what and where something happens around them with their hearing, as long as sound frequencies lie between 20 Hz and 2,000 Hz. Researchers at Aalto University have now developed a new audio technique that enables people to also hear ultrasonic sources that generate sound at frequencies above 20,000 Hz with simultaneous perception of their direction. The results have been published in Scientific Reports on 2 June 2021.

'In our study, we used bats in their natural habitat as sources of ultrasonic sound. With our new technique, we can now hear the directions-of-arrival of bat sounds, which means we can track bats in flight and hear where they are -- we're essentially giving ourselves super hearing,' says Professor Ville Pulkki from Aalto University.

Small devices have been used before to listen to bats but previous versions haven't allowed listeners to locate the bats, just hear them. With their device the researchers record ultrasound using an array of microphones flush mounted and uniformly distributed on the surface of a small sphere. After the signal has been pitch-shifted to audible frequencies, the sound is played back on the headphones immediately. Currently, the pitch-shifting is performed on a computer, but, in the future, it could be done with electronics attached to the headphones.

'A sound-field analysis is performed on the microphone signals, and as a result we obtain the most prominent direction of the ultrasonic sound field and a parameter that suggests that the sound comes only from a single source. After this, a single microphone signal is brought to the audible frequency range of human hearing and its single-source signal is played back on the headphones so that the listener can perceive the source from the direction the sound was analysed to arrive,' Pulkki says.

On top of its popular appeal, the technique has tangible real-world applications.

'In science and art, people have always been interested in how they could improve their senses. Finding sources of ultrasonic sound is also useful in many practical situations, such as finding leaks in pressurized gas pipes. Minor pipe leaks often produce strong ultrasound emissions not detected by normal hearing. The device allows us to spot the sound source quickly,' Pulkki explains.

'Sometimes, damaged electrical equipment also emit ultrasound, and the device could be used for locating faulty equipment faster in places such as data centres,' he continues.

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It took us almost two months to comb through dad's house, sorting the myriad pieces of his unpursued passions into several appropriate piles for disposal.

• Keep.
• Sell.
• Donate.
• Trash.

He didn't have much in the way of food, but cookbooks in mint condition spilled out of his kitchen cupboards. Mystery novels were stacked neatly on his bedside table, suffocating under layers of dust. Princess Di's biography and Stephen King's The Shining lay face down on the coffee table, spines cracked towards the ceiling. Poets hid, forgotten, behind the basement bar. Daunting masterpieces of Joyce, Hugo, and Dumas stood proper and pristine in the bookcases of his spare bedroom. Harry Potter, curiously, was lined up neatly on the workbench in his garage next to an impressive collection of equipment manuals. Donate.

While I examined every paternal artifact with the zeal of an amateur archaeologist, my sister, Kate, executed our job grudgingly, methodically, the corners of her mouth tugged down in mild distaste. She held no curiosity for the life that gave us life, and I assumed her interest in him extended only as far as his had in her.

We waded through a world of short-lived hobbies. The shed in the yard boarded gleaming gardening tools, unspoiled art supplies, and a pair of cross country skis still marked with a discount sticker. Sell.

We purged every nook and cranny in the house of unused useful treasures. Three hundred glass mason jars collected dust and spiders in the alcove under the stairs; forty-five rolls of scotch tape curled up on their sides, stacked haphazardly in the cupboard above the washing machine; three five-gallon pails of assorted nails, screws, and bolts rusted behind the furnace. Keep. Donate. Trash.

A Yamaha keyboard piano emerged from under piles of forgotten laundry. Sell. Beginner sheet music for the guitar we'd never heard him play was buried in a wicker basket under a cascading mountain of magazines. The guitar in question was wildly out of tune. I strummed a dissonant chord absentmindedly, prompting Kate to grab and drop it with a reverberating hum next to a harmonica, a violin bow, and an assortment of small percussion instruments. Donate.

"We could sell that!" I exclaimed.

"He bought it at Walmart," she replied flatly, and I briefly wondered how she knew.

Dad hadn't been a bad guy, as far as I remember. I recalled him doing all the right dad things "teaching me to throw and catch a ball, taking us to the county fair to eat too much candy, bringing home a wriggling bundle of floppy ears and sad eyes that we crossed our hearts to feed, train, and walk (naturally, and much to her disgruntled dismay, it became mom's exclusive responsibility)".

It was just that, between the checked boxes of fatherhood, absence was his only constant.

Early on, it was missed birthdays, disappointing Christmas mornings, and an empty seat in the stands at my B Division hockey games. By the time I was ten, he banged through our door only once or twice a year. Kate would quietly disappear to a friend's; mom would gravitate as if on auto-pilot into the kitchen to prepare a meal; I would hover, eager to brief him on my latest activities and accomplishments, hopeful he would finally divulge something about the band with which he was surely traveling, or the secret mission on which he must have been deployed. "This and that" was all he ever offered.

When Kate left home, he came around even less often.

I waded into the unmired moodiness of my teenage years and developed (feigned) indifference in his disinterest. By the time I crashed clumsily from adolescence to adulthood, dad was a sort of non-entity that flitted and fluttered at the edges. He attended my university convocation, but didn't stick around for the celebratory dinner. He stood by us at mom's funeral, appropriately sad, but left us to make the arrangements and deal with her estate. He was invited to Kate's wedding, but she asked me to walk her down the aisle.

At Kate's orders, I tackled the bedroom, while she disappeared for days under unreasonable hoards of wooden spoons, tacky coffee mugs, and canned goods. The stench of sickness still clung to his mattress and its clothes. Trash. The neglected novels on his bedside table were jacketed in dust and blanketed in crusty tissues. Trash. Drawers were mostly empty save for a rolling lip chap and a handful of loose change. The rest of the furniture appeared in fine health. Sell.

Rifling through his closet, I found only a few crumpled receipts in the pockets of his clothes. Donate. My climbing bewilderment and disappointment reached their peak. A lifetime of pretending not to care aside, we finally had unfettered access to the private life of our flighty father. I wanted to find a trunk of sentimental memories in his basement, or a shoe box of photographs labelled with hard-to-read names stuffed in the closet, or a stack of secret-littered journals on the bookshelves. But the modest 900 square-foot house rejected my foolish fantasies.

Last year, Kate had learned dad was unwell. "Oh, by the way," she hesitantly tacked on to our annual phone call, "Dad's been in the hospital."

I paused, caught off guard by her mention of his existence and, further, her awareness of his illness. I'd wanted to know more "what was wrong, should we go visit, who was taking care of him, who called her" but my tyrant nephews were wailing in the background, and she took advantage of my silent beat to skewer the conversation. "He's fine now, at home, I guess. Listen, don't worry about it" She trailed off as the cacophony of family anarchy rose with a mighty crescendo, and the line died.

I didn't call back, and neither did she. The next time we spoke, she delivered a dispassionate dispatch. "He's dead."

Now we stand among life's leftovers.

• Keep. Empty.
• Sell. Posted.
• Donate. Boxed.
• Trash. Bagged.

There is no heirloom-worthy jewelry. There are no old family photos. There aren't any accolades or love letters, not even a final will and testament. Nothing in seventy years' worth of accumulation sheds a shred of light on who dad was or why.

I watch my sister lug bags and boxes out the door, and wish there was someone left who knew him.

When the trucks are packed and the house echoes in vacant relief, we stand on the front porch and watch the realtor pound a For Sale sign into the frosty lawn. I mutter, "I should have gone to see him, you know, before&"

Kate turns and looks up at me with the most peculiar expression of incredulity. She puts her gloved hand on my arm. For a long quiet moment it feels like she's trying to convey something important, but all she leaves me with is: "See you at Christmas."

And then she's gone without looking back, bounding down the cracked concrete towards her car with a lightness in her step I've never seen before.

Credit: Christina Marie

Despite a name straight from a Tarantino movie, natural killer (NK) cells are your allies when it comes to fighting infections and cancer. If T cells are like a team of specialist doctors in an emergency room, NK cells are the paramedics: They arrive first on the scene and perform damage control until reinforcements arrive.

Part of our innate immune system, which dispatches these first responders, NK cells are primed from birth to recognize and respond to danger. Learning what fuels NK cells is an active area of research in immunology, with important clinical implications.

"There's a lot of interest right now in NK cells as a potential target of immunotherapy," says Joseph Sun, an immunologist in the Sloan Kettering Institute. "The more we can understand what drives these cells, the better we can program them to fight disease."

First in Line

Previous work from researchers at MSK and elsewhere has shown that T cells rely on aerobic glycolysis to carry out their protective functions. But whether NK cells depend on this form of metabolism to power their own activities was not known.

Because Dr. Sun and his colleagues studied NK cells in animals instead of a dish, they could establish what type of metabolism NK cells use and compare it to T cells in a natural setting. They found that NK cells ramp up aerobic glycolysis about five days prior to when T cells respond with their own glycolytic surge.

"This fits with the idea that NK cells are innate immune cells that are really critical for mounting a rapid response," Dr. Sheppard says.

The findings are relevant to ongoing efforts to use NK cells as immunotherapy in people with cancer and other conditions. In particular, they have implications for using NK cells as a form of cell therapy -- when cells are grown outside a patient and then infused back into the patient's blood.

"If you're growing these cells in a dish and you push them to divide too rapidly, they may not have as much potential to undergo aerobic glycolysis when you put them into a patient," Dr. Sheppard says.

The takeaway for researchers designing clinical trials is this: They must find a balance between encouraging NK cells to multiply and preserving their stamina. These NK cells are the paramedics of our immune system, so it's important to keep them speedy and responsive.

The findings were reported June 1, 2021, in the journal Cell Reports.

This research was supported by the Cancer Research Institute, the NCI Cancer Center Support Grant (P30CA08748), Cycle for Survival, the Ludwig Center for Cancer Immunotherapy, the American Cancer Society, the Burroughs Wellcome Fund, and the NIH (grants AI100874, AI130043, AI155558). The study authors declare no conflicts of interest.

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