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Water isn’t stored at all in the tear ducts. Tears are made “on demand” when anything from a sad emotion to dust in the eye triggers stimulation of the tear glands. Contractile cells in the lacrimal gland then force the fluid down into the ducts as it is made. It doesn’t stay or accumulate in the ducts.To be candid, I don’t know the composition of tears very well. Water, certainly, and they also contain an antibacterial enzyme called lysozyme, antibodies in the IgA class, mucus, and oxygen, which supplies the cornea. There are electrolytes in the tears as well. They also contain a bit of oil, but that’s added by tarsal glands on the inside margins of the eyelids after the secretion has left the tear glands—so you could detect that in tears sampled from the medial corner of the eye or from the lacrimal sac or nasolacrimal duct, but I don’t think any would be found in tears sampled at the lateral corner of the eye, fresh out of the gland. The oil and mucus keep the tears from evaporating too rapidly, thus helping in most people to prevent dry eyes.Here’s my textbook illustration of the lacrimal apparaus.Below is a microscopic image[1][1][1][1] of the tear gland’s mucous cells—the light pink, foamy looking cells. “M” indicates a myoepithelial cell, one of the contractile cells I mentioned that squeezes the glandular sacs from within, forcing the tears to flow down into the ducts.Here is another photo of lacrimal gland I found,[2][2][2][2] this one showing only serous cells (smaller, denser, and staining darker pink). Serous cells in mixed glands like this secrete a more watery, less mucous product. The white spaces at the center of each circular cluster of cells are the beginnings of the duct system.Footnotes[1] Figure (1): An acini; The mucous secretory cells of the gland, has a...[1] Figure (1): An acini; The mucous secretory cells of the gland, has a...[1] Figure (1): An acini; The mucous secretory cells of the gland, has a...[1] Figure (1): An acini; The mucous secretory cells of the gland, has a...[2] Lacrimal Gland Tumors — Ophthalmology Review[2] Lacrimal Gland Tumors — Ophthalmology Review[2] Lacrimal Gland Tumors — Ophthalmology Review[2] Lacrimal Gland Tumors — Ophthalmology Review

I’ll assume that by “Actor-Critic” you mean “Stochastic Actor-Critic (SAC)”. Both SAC and DDPG implement a model-free policy gradient and value based method. But, eponymously, SAC represents the policy as a parametric probability distribution (stochastic approach)[math]\pi_{\theta}(a|s)=Pr(a|s;\theta)[/math] whereas, the DDPG learns a deterministic policy [math]\mu_\theta(s)=a[/math]. The gradient theorems that these two follow are also kind of different. SAC incorporates the Stochastic Gradient Policy Theorem:[math]\nabla_{\theta} V(\pi_{\theta})=E_{s\sim \rho^{\pi},a\sim \pi_{\theta}}[\nabla_{\theta} \log \pi_{\theta}(a|s) Q^{\pi} (s,a)][/math]So, it’s calculating the expected gradient of the log-likelihood of the [math]Q^{\pi}[/math] value if we start from the state [math]s [/math][math][/math][math][/math]and act according to the policy [math]\pi_{\theta}[/math] with respect to parameters [math]\theta[/math].The DDPG follows a deterministic policy version of the above theorem called the Deterministic Gradient Policy Theorem:[math]\nabla_{\theta} V(\pi_{\theta})=E_{s\sim \rho^{\pi}}[\nabla_{\theta} \mu_{\theta}(s)\nabla_{a} Q^{\mu} (s,a)|_{\mu_{\theta}(s)=a}][/math]Notice how this theorem only integrates over the state space and not the action space. This gives DDPG an edge over its stochastic counterpart:DDPG could perform more efficiently than SACDDPG can outperform SAC in higher dimensions.SAC could require more samples than DDPG if the action space has many dimensionsBut as should be clear from the theorem: DDPG limits exploration. To battle this: one needs to introduce off-policy learning algorithm so that the learning agent can explore the state-action space satisfactorily.Finally, here’s how I really think the Actor-Critic algorithm works::)

It doesn't necessarily have to be the ring finger from the left hand. Blood can be drawn from either the ring, middle or index finger of any hand, but usually its preferred to draw it from the ring finger of the non-dominant hand(in most cases left hand) since that's least likely to affect our capabilities to perform day to day activities.You might be wondering then why don't we use the little finger. Infact that would have been a better option compared to the ring finger. However anatomy tells us otherwise which is clear from the picture below:See how the radial and ulnar bursa extend up to the tip of thumb and little finger respectively.Bursa - It is a fluid (synovial fluid) filled sac lined by synovial membrane usually situated in places in tissues where friction would otherwise occur.Now imagine that if while trying to get a sample of blood an infectious organism somehow managed to enter your system. It invaded the bursa and spreads from the tip of your finger all the way upto your wrist. You don't want that right? The person taking your blood sample doesn't want that to happen either. That's why we prefer the other 3 fingers.Now, if you see the image clearly you can see that the synovial sheath in the other 3 fingers are only localised to that finger so any infection here stays in that finger only. Even with the best precautions there is always a chance of something going wrong and no-one wants to take that risk especially for something so trivial as drawing blood. No person in his right mind would want to complicate things by trying to use the little finger. Its just inexcusable(unless circumstances calls for it). So we all prefer to use the index, middle or ring finger for taking small samples of blood. The ring finger is always the most popular though.