Excitation of Faraday-like Body Waves in Vibrated Living Earthworms

Иконка: Аннотация Ivan S. Maksymov, Andrey Pototsky

Firstly, for the fundamental subharmonic resonance in our model we choose the doubled frequency to be ω0 = πfmin, where fmin is either 38 Hz or 43 Hz corresponding to the first and the second minimum of the measured critical vibration amplitude function. Then, for any fixed value of E we find all theoretically possible vibrational modes whose doubled frequency Pic.: w0pi differs by at most 1 Hz from either 38 Hz or 43 Hz. We choose the tolerance of ±1 Hz because it corresponds to the frequency resolution in the experimental data in Fig. 4. It is noteworthy that our model predicts another upper bound for E when the tolerance is varied. However, choosing the tolerance dictated by the resolution in the experimental data serves the purpose of comparing the experimental and theoretical results obtained in this work.

Denoting the number of modes that match 38 Hz and 43 Hz as N38 and N43, respectively, we define the total number of matches as N = N38N43. Finally, by gradually varying E with a fixed increment, we obtain the dependence N(E) and plot it in Fig. 6. We observe that the largest possible value of the Young’s modulus lies in the E = 8.3 … 8.9 MPa range, which corresponds to the mode excited at f = 38 Hz and the mode excited at f = 43 Hz. The corresponding values of the frequency factor are shown by the two horizontal lines in Fig. 6. Based on these results, we predict that the body of the worm subjected to vertical vibration and undergoing Faraday-like body oscillations would assume the spatial profiles shown in the insets in Fig. 6.

The values of the Young’s modulus E = 8.3 … 8.9 MPa produced by our model feasibly fall within the expected range. In fact, these values are approximately one order of magnitude higher than those of the effective bulk Young’s modulus of the worm predicted in [53], being at the same time one order of magnitude lower than those obtained from local measurements of the stiffness of the cuticle [60, 61]. This is consistent with the point of view that the effective mechanical properties of the worm are not exclusively defined by the stiffness of the cuticle. However, we also conclude that the cuticle plays a considerable role in the response of the worm to vibration.
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We have demonstrated the excitation of subharmonic Faraday-like waves in living earthworms lying horizontally on a flat solid surface subjected to vertical vibration. We tested four common species of earthworm – Eisenia fetida, Lumbricus terrestris, Lumbricus rubellus and Aporrectodea caliginosa, and in all tests we observed the appearance of spectral peaks at subharmonic frequencies with overall behaviour similar to that of finite-size liquid drops subjected to vibration. We also used an earthworm-mimicking phantom made of a water-filled cylinder with thin elastic walls, the measurements of which qualitatively reproduced the response of the real earthworms. Moreover, we measured the critical amplitude of the onset of subharmonic waves in the worms and found that it exhibits oscillations as a function of the driving frequency. This feature is typically observed in the response of infinitely extended viscoelastic fluids [54] and isolated small drops composed of a Newtonian fluid [30, 31, 32, 33]. By modelling the body of the worm as an elastic cylindrical shell filled with fluid, we explained the observed subharmonic response by parametric excitation of the discrete set of vibrational modes. We therefore conclude that the nonmonotonic dependence of the critical amplitude on the vibration frequency should be a direct consequence of the discrete nature of the spectrum of eigenfrequencies.

Because biological cells and many living organisms are mostly made of fluids, unique properties of nonlinear waves observed in fluidic systems are likely to open up unique opportunities for biology and medicine as well as the adjacent areas. The work in this direction is already in progress [44, 55]. Thus, we believe that our results would not only push the frontiers of our knowledge of fundamental nonlinear phenomena and chaotic behaviour in biological systems, but they could also be used to develop new techniques for probing and controlling biophysical processes inside a living body.

For example, it has been suggested [69] that Faraday-like body waves in vibrated living earthworms could be used to verify the soliton model of nerve pulse propagation [4, 5]. Mechanical stimulation has long been used to excite nerve impulses [70], but so far this has not enabled researchers to establish a reliable link with the brain. The ability to form a soliton in the nerve may not necessarily mean that solitons underpin the principal natural mechanism for nerve impulse propagation. However, the demonstration of soliton existence in externally excited nerve fibres would be a paradigm shift in the way we understand the nervous system [4, 5]. As shown in this paper, Faraday-like body waves in living earthworms may have 20 – 300 Hz frequencies coinciding with those of natural nerve impulses. Thus, hypothetically, constructive or destructive interference of these waves with nerve impulses could be used to amplify or suppress the nerve signalling in a living worm69, which in turn should open up novel opportunities to control nerve signals mechanically.

Finally, we note that in neuroscience experiments the worm is often anaesthetised to inhibit the generation of natural nerve impulses [14]. We experimented with non-anaesthetised and lightly sedated worms and we also observed the onset of Faraday-like body waves in many cases. However, whereas this result indicates that the results presented in our work should also apply to non-anaesthetised worms, it is very challenging to keep the worms in the focus of the laser beam and therefore experimental data are difficult to interpret and analyse using the available mathematical models.

We also note that our theoretical model remains valid in case of non-anaesthetised earthworms having higher internal pressure. As a result, the linear approximation Eq. neglecting the squashing depth becomes even more accurate because the squashing depth in Eq. is further decreased. Because natural frequencies of pressurised elastic cylinders increase as compared with those of low-pressure elastic cylinders [71], in non-anaesthetised earthworms the minima in the critical vibration amplitude in Fig. 4 should shift to higher frequencies.
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The hardware used in our experimental setup is similar to that in [38]. Because the maximum frequency of interest in this work is about 200 Hz, we used a photodiode designed for general applications in sensors and laboratory instrumentation. The photodiode is sensitive to the light in the broad 400 … 1100 nm spectral range with the sensitivity peak around 750 nm. The maximum frequency response of the photodiode measured using our laser diode controlled by an electronic driver circuit is 14 kHz, which is well above 200 Hz. Photodetector data were acquired using Audacity, a standard digital audio recording software that is often used for research purposes [14]. Overall, at low vibration frequencies and other similar experimental conditions, the accuracy of our setup is comparable to that of a commercial laser Doppler vibrometer.

Because of the low vibration frequencies, a consumer action camera providing the resolution of 1280 × 720 pixels at 120 FPS speed was able to resolve the frequencies of the harmonic and subharmonic response of the body of the earthworm. Moreover, this camera is waterproof and easy to clean, which is important in research on animals, and it is also equipped with a 140° wide lens that allows capturing more ambient light, thereby dramatically improving the resolution as compared with a standard high-speed digital camera recording at up to 1000 FPS at the same illumination conditions.

Data produced by the camera were processed using the FFmpeg and GNU Octave software. Because in all experiments our setup operated in a regime of moderate vibration amplitudes, approximately 30-second-long videos of vibrated worms were not affected by significant motion of the worm with respect to the centre of the camera’s field of view. Long worms were bent to maximise the portion of their body captured by the camera. However, the curvature of the worm’s body did not affect the results of our analysis. Because all liquids surrounding the worm were carefully removed before each measurement using a syringe and cotton wool tips, the standard GNU Octave command bwboundaries alone allowed finding the contours of the worm without the need of removing artefacts.
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Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.
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This work was supported by the Australian Research Council through its Future Fellowship.

The text is published by Scientific Reports

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Ivan S. Maksymov, Andrey Pototsky. Excitation of Faraday-like Body Waves in Vibrated Living Earthworms. Page 1     2     3     4    5

Anna Henschel. Science has a Mean Girls Problem

Окончание К началу
   Here are some practical examples of these proposed benefits. Hopefully, you’ll see that you don’t, in fact, have to be an interdisciplinary researcher to take advantage of them.
Thinking outside the box
   Let’s take a little pop quiz: Who was the scientist who in 2016 first recorded gravitational waves?
   Did you know that, similar to the recent image of a black hole, a large team of scientists from various disciplines was behind this big jump forward in human discovery and knowledge? In fact, some researchers argue that the power of team science can be harnessed beyond Physics and can be applied to solve many of the problems the field of Psychology struggles with at large.
   With this idea in mind, the Psychological Science Accelerator was born – the CERN for Psychology. This large-scale network of researchers across the world aims to tackle two important issues in psychological science: small and WEIRD participant samples. Research projects are proposed to the PsySciAcc and the ones that are selected are conducted across many labs, with scientists following the same experimental procedure in Kenya, Malaysia and Ecuador to investigate, for example, the Valence-Dominance Model of Social Perception.
Shared experiences
   Another benefit relates to a topic I want to call the struggle is real:
   I recently read a book by the Edinburgh-based palaeontologist Steve Brusatt, and found myself chuckling at many of the anecdotes he describes when it comes to conferences, talks, undergraduate life, tales of scientific feuds and the sweet ‘eureka’ moment of discovery.
   And while my personal experience with digging up dinosaur bones is unfortunately limited, I think we can agree that academia is a special ecosystem, associated with some struggles that people can relate to everywhere. If you have ever felt a bit awkward or out of place in a room full of senior academics, were nervous before a talk, or hesitated to raise your voice in a discussion, you can connect with early career scientists from any discipline, whether this is STEM or the Arts and Humanities.

Pic.: via Giphy

   Many more examples underline the idea that keeping an open mind towards other fields of research and different methodologies can lead to more human connections and better scientific outcomes.
   As scientists, we cannot control where curiosity leads us. What we can control, and what we all share, is a desire to find the truth and to advance shared knowledge. In these divisive times, it can be reassuring to focus on the things that unite us as a community, not those that drive us apart. Let’s try to be a little less Mean Girls and a bit more Breakfast Club.
The text is published by University of Glasgow PGR Blog
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Christopher R. Chiodo, Kimberly K. Broughton, Max P. Michalski. Wit and Humor During the COVID-19 Pandemic

From Editorial Board

Pic.: Covid Quarantine

   At a time when the entire world of humanity including T.C.A. Editorial Board is in quarantine over COVID-19, three American surgeons are talking about wit and humor during the pandemic …
   If there ever was a time in our lives that we could use a smile or good laugh, it’s probably now. Thousands have died, and each day, the headlines grow more bleak as the COVID-19 pandemic progresses. Hopefully, the curve can be flattened and lives saved. This process will take time, however, and as such, we are likely facing a prolonged crisis that will last several months.
   In the setting of this unfolding calamity, we are faced with so many critical questions. One that might be easily overlooked is the current role of humor in our professional lives. The importance of this question derives as much from our roles as team leaders, as it does our status as physicians.
   Given the potential for humor to relieve tension and settle frayed nerves, is now a better time than any to offer a witty comment to a colleague or your team? On the other hand, might that same witticism be frowned upon given our temporal and physical proximity to so many sick and dying individuals?
   While this may feel a bit like standing in front of the Oracle at Delphi, the 2 positions may not be so diametrically opposed and can be reconciled with some careful thought. More specifically, it may be possible to still employ wit and humor but with some important checks employed. Yes, that fatigued and stressed colleague could certainly benefit from a smile. However, there are some new considerations that must be taken into account while trying to brighten a moment during the current crisis. In formulating the principles delineated below, we’ve reached out to some brave and inspiring colleagues who are at the front lines of the current pandemic.
   Tone it down, but don’t turn it off. Last week, there was palpable tension among the receptionists and medical assistants in our office. After a few words of encouragement and thanks, there seemed to be something missing. Clinics are generally lighthearted and fun. After a quick joke about the poor ham sandwich who couldn’t get a beer at the bar because the bartender said he doesn’t serve food, the tension eased. Everyone smiled, a few laughed out loud, and one person went out of her way to say thanks. For the rest of the day, though, it was a more somber environment, appropriately so. After all, there is always the risk of being considered silly if humor is used too frequently. That rule is even more important now, and the “silliness threshold” is likely lowered. One nurse from the hard-hit Los Angeles region reported, “Humor is still alive in our ICU. It helps unify us, makes you feel you are a part of a team, and not so isolated in a lonely time. . . . As a member of a pretty close knit team I feel that making jokes is part of my job. I have not let up . . . I know it lightens the heaviness we feel in our chests on a daily basis. But when things hit the fan, we all work hard. No joking during that time.”
   Always try to laugh with, and not at, someone. Professor Rod Martin is a clinical psychologist from Canada who is an authority on the benefits of humor. Countless schemes have been derived to classify humor, of which his is one of the most well known. He divided humor styles as either being benign or injurious.2 Along these lines, it is generally safer to laugh with each other, rather than at someone. Laughing at someone invokes the superiority theory of humor, which is socially dangerous, harmful, and detrimental to teams.
   The exception to this rule, however, is the use of self-defeating humor. While this type of humor may not always fit into the workplace, showing self-vulnerability in challenging times may ease the tension of others around you. Because self-defeating humor may be interpreted as ineptitude by a patient or anxious family, it is best reserved to be used among colleagues as a means of lightening a moment and enhancing your relationship with the team.
   Gallows humor is okay; just be careful. Gallows humor includes jokes, irony, and humorous remarks about frightening topics such as combat and death. An active pandemic presents ample opportunity for the use of this form of humor. For some, gallows humor is a coping mechanism that may also boost camaraderie and morale.
   However, it may also portray a clinical scenario as more grim than it really is. Joking that we’re all going to die from COVID-19 is obviously a gross overexaggeration and one that may increase anxiety among less informed members of a team. Another danger of gallows humor is that it may be overheard by an “outsider” who is offended, threatened, or caused to unnecessarily worry about a situation. Imagine an inpatient overhearing health care providers employing gallows humor about increased workload or a bleak prognosis.
   When we spoke with an active emergency medicine physician who has also led previous global disaster responses, she commented that gallows humor may actually be helpful when used carefully, and front-line providers shouldn’t have to feel guilty about using it. You just have to understand that it has a time and place.
   Make it quick and short. The members of a care team may be increasingly busy and stressed and may not have the time or emotional bandwidth to digest a long anecdote or complex joke. Irony, witty comments, and even “dad” jokes may represent simple aliquots of humor and brevity that will be just enough to brighten the moment without crossing the silliness threshold.
   Quips and carefully placed momentary sarcasm can also be quick ways to bring about a smile or laugh. Remarks that take a surprise twist or unexpected perspective can get others out of mental ruts that occur during a crisis. The comments others “didn’t see coming” can be used to positively derail a dreary situation.
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