Wednesday, February 26, 2014

Fish report


One of the highlights of this winter has been my membership in a new seafood co-op.

Each week I go to the farmers’ market to collect my pound of fresh-catch, bring it home, cook it, and feed it to my family. The first week was angel shark, and I gave it my standard fish treatment (recipe below). Next was pacific rockfish, often sold as “pacific red snapper”. This was made into a farmers’ market ceviche, with a variety of market citrus. The third week’s catch was a big hunk of swordfish, which I divided into three steaks, and gave my standard fish treatment with cilantro sauce. Last week was mussels. I sautéed up an onion and head of garlic in half olive oil/half butter while I scrubbed the mussels, and trimmed their beards. Then into the skillet they went along the remaining wine in my glass. I covered the skillet and threw the fresh pasta into a pot of boiling water. I drained the pasta, poured it over the mussels (now perfectly steamed and waiting in their open shells) and mixed in some miso and grated ginger. Delicious.

Recipe: Standard fish treatment for prepared filets or steaks. (oil plus two toppings)

Preheat oven to ~350
Prep fish: pat dry on a towel, salt & pepper, and perhaps a dusting of flour if it’s a thin fish.
Put the fish skillet on the stovetop on a hot flame. 
(I have a few: these are oval-shaped oven-proofed skillets with a handle)
When skillet is hot, add a generous splash of oil and a generous pat of butter.
Plop fish in the skillet. The oil & butter will splatter all over.
Put the oven's top-broiler on.
When fish is halfway done, put on topping 1, and place under the broiler.
When fish is almost done, take out of the broiler & put on topping 2.
Serve in the hot skillet. Fish will finish cooking as you herd your family to the dinner table.

Some of my favorite combinations of oil/topping 1/topping 2
Butter/capers/lemon & parsley
Peanut oil/sesame oil & green onions/lime juice & grated ginger & soy sauce
Ghee/curry & yogurt/cilantro
Olive oil/curry & salsa/parsley
Olive oil/salsa verde/
Olive oil/capers & tomatoes& shallot/parsley & lemon
Butter/shallots/miso & rice wine vinegar

Aqueous reduction reactions


Next in a series of blog posts about one of my favorite subjects, electrochemistry.

The hydrogen evolution reaction is one of the most famous chemical reactions there is. On a water planet like ours, it is the most important reduction reaction.

So, if something is oxidized in water:
            M = M++ + 2e-

Then there are basically only four choices for the reduction reaction.
If oxygen is present, then the reduction reaction is always:
½ O2 +2e- = O-2
In acidic water, the reaction is 2H+ + ½ O2 + 2e- = H2O
In basic water, the reaction is H2O + 1/2O2 +2e- = 2OH-

Note that in acidic water, the reduction reaction of O2 neutralizes the acid.
While in basic water, the reduction of O2 makes it more basic.
Reduction of O2 to O- always moves the pH of the solution up.

But that’s only if oxygen is present.
When oxygen is absent H+ must be reduced in an aqueous system.
This happens at far lower potentials—it takes a lot more energy to make 2H+ take two electrons than  1/2 O2 to take two electrons. (in fact—you can think of oxygen as grabby when it comes to electrons. It’s why breathing feels so good.)

In an acidic environment: 2H+ + 2e- = H2(gas) which bubbles out.
In a basic (or neutral) environment: 2H2O + 2e- = H2 + 2OH

Note—again in both of these reactions, the water evolves to a higher pH—less acidic, more basic.

Questions to consider: Does this mean that the change in pH of the oceans over geologic time is a fundamental marker indicating whether the surface Earth is becoming more or less oxidized?
So: if oceans are increasing in acidity—that means that the Earth is reducing (so ocean rxn is to oxidize). Or if oceans are decreasing in acidity—that means that the earth is oxidizing with time?  

As you consider this question, remember that CO2 is also a big player in the ocean-climate story, adjusting the pH and water chemistry.

In an upcoming post, I examine the hydrogen evolution reactions in some more detail.

Sunday, February 16, 2014

Recent Visit to Mars


I had an opportunity to dig up old data & analysis on the Mars interior for a recent meeting. It was fun on many levels.

First, there’s the fascinating Mars interior with its huge transition zone. Is it drenched with water? Does it show evidence of compositional as well as structural changes? And Mars D double-prime (aka the core-mantle-boundary) is fun to ponder. A single measurement of the core radius will tell us whether there is a transition to perovskite at the bottom of the Martian mantle. A phase transition right at a huge chemical and (likely) thermal boundary layer is interesting—because it will either amplify or dampen instabilities—and therefore help govern dynamics. 

A single data point for the position of the Mars core-mantle boundary will tell us a huge amount about the thermal, mechanical, and chemical history of Mars.


Left: Earth interior density vs. pressure on a log-log scale, so the important parts (for Mars) are emphasized. Right: my preliminary Mars interior density model, based on Earth's, but with 1. low velocity zone removed and 2. increased density of mantle material, due to SNC meteorite constraints suggesting there's more iron in the Mars interior. Depending on the size of the core (which depends on sulfur content to fit mass and moment of inertia constraints), there is either a perovskite layer at the base of the mantle (small, iron-rich core) or not (larger, sulfur-containing core).
 The Mars transition zone is interesting also. On Earth, the transition zone is a relatively small sliver of the mantle, but it's interesting because the steep seismic velocity profile shows that the mineral assemblage is changing throughout this zone. Is it purely a structural evolution (SiO4 tetrahedra to SiO6 octahedra within the garnet) or is it compositional also (e.g. Fe changing? Mg/Si ratio changing?). On Mars, this mineral assemblage makes up the bulk of the lower mantle--and therefore a significant portion of the Mars interior. A measurement of the depth-dependent velocity of the transition zone will also tell us a lot about Earth and Mars.

A mineralogical model of the silicate mantle of the Earth (and Mars).
The minerals that make the transition zone: silicate spinels and garnets happen to be able to store a lot of water in their structures. Up to a percent or so. That's the rock equivalent of a wet sponge. So--if water can get down to the martian mantle, or if it was there and never left, there is the possibility that the Mars interior may store a huge amount of water relative to its surface, and relative to the amount the Earth's interior might store. This could be important for rheology, partial melting, and electrical conductivity. Water softens everything.

Then, there was digging through the old pictures of data collection at the synchrotron. My colleagues Dan and Wendy are there (were they both grad students then?) and a smiling Abby showing off her big baby-bump at the synchrotron. I think I might have been the first pregnant user at the APS, and people wearing ties came to discuss it with me and with the PI of the beamline. See I’m the only one wearing a dosimeter? They checked and rechecked every corner of the hutch with Geiger counters before my time started. I also worked while pregnant at the NSLS. The floor manager met with me before my time and said: it’s safe to go almost everywhere most anytime. Just don’t go near this area during insertion. (I forgot the exact, just remember the gist).

Dan Shim, Wendy Panero, and Abby Kavner  late 1998
The measurement was a high pressure and temperature phase stability and equation of state for FeS, the sulfur-rich endmember of our best guess of Martian core composition—likely along the iron-iron sulfide join. I analyzed the data, developed a model of the Martian interior, and wrote a draft of the paper during maternity while I was nursing my son.

The icing on the cake was that revisiting the science, the data, the history this week coincided with my son’s 15 birthday. So in parallel, I was able to reflect on 15 years as a mom-scientist. He’s thriving as he should, and my mom-heart overflows. My science-heart also pounds, but in different ways than it did 15 years ago. I am still a striver, but my definition of thriving is changing.

It's Alright to Cry


Dear students, colleagues, and others who cry in my office: Not a problem. I’m such a crier myself, I’m almost relieved when you join me. This is a situation I understand. Since my own personal threshold for crying is so low, I never assume that you are necessarily close to or at the end of your tether. Just that you are a person with emotions that you are able to express. I consider myself relatively fluent in the expression of emotions (except anger, which still confounds). Here are some of the emotions that make me cry: Sadness, frustration, anger, Feeling hurt by others, missing someone dear, physical pain, others' illness. Nostalgia. Bad news or sad news. Empathy. Hope Jahren’s blog posts. Crying children. Singing children. Newborn children. Nature. Competence. Good data and/or data analysis. Successful feats of engineering. Art and music.  When I’ve finished the last page of a good book.

http://www.youtube.com/watch?v=Y52bs0aX6v8&feature=kp